How To Build A Teardrop Trailer/Walls and Doors
At this point in your build, you should have an assembled trailer frame (less lights, fenders, and fender braces), with a nice wooden bed bolted in position. The bottom of the bed is protected with roofing tar.
Polyurethane glue is going to be an important part of the trailer construction. It fills gaps, is not brittle (like yellow wood glue) and is extremely binding and strong. So strong that the force applied to a piece of 2x2 pine wood which was polyurethane glued to cabinet grade .75" plywood for only 30 minutes actually took the first ply off the wood, but not before splitting the plywood down the middle.
The difference between this teardrop trailer body and just a simple box is that the body walls, roof and bed will be bonded together with this polyurethane glue, in essence creating a monocoque. In addition, the teardrop shape of the roof line increases the strength over a square box because forces are transferred around the curves down to the base.
You need to spend some time and pick out a profile for your teardrop trailer. There are many variations of profiles and some have names like "benroy", "modern" but there are really only two classes of sidewalls - those which come down perpendicular to the bed and those which curve out beyond the front of the bed then curve back to it. And these are used in combination also. The modern profile has both front and back curving out and back like an airplane wing. The benroy front and rear meet perpendicular to the bed. Others use the out and back curve on the front and meet the bed perpendicular at the rear. Yet others do the opposite.
You really should take the time to explore what you like and design your own variation. The profile of the teardrop trailer is the most distinctive and artistic part. It defines the trailer and can either make onlookers say "Wow!" or "Ugh!".
One other thing, the cabinet grade plywood has a good side and a bad side. Its up to you but you should really put the good side out unless you are going to skin the trailer or paint it. This book doesn't cover skinning or painting. Our "simple" trailer is a "woodie" that will be covered with marine grade urethane varnish.
Also when you are drawing your profile on the wood you should draw it on the "inside", because a sabor-saw cuts on the upstroke and the exit side of the cutting blade is the side that has the rough edges. You want the "outside" to have the cleanest cut edges.
You also need to decide on a door shape. Again there are many variations. Some are completely square. Some have a straight edge on hinge side and a straight edge across the bottom, and have a long side arch opposite the hinge side. Some have a simple arched top or rounded corners. Other variations exist and are possible.
You need to put some thought into the door shape, the hinge and how you are going to place a door seal. The door shape will have an impact on the type of hinge you use and whether you can seal from the outside or not.
- There are three styles of hinges commonly used for teardrop trailers.
- Regular house style hinges
- A piano hinge.
- Gate hinges
A regular house style hinge requires that a door jam be constructed deep enough to accommodate it. On the plus side there is nothing custom or experimental about it. You create the door and jam just like on a house.
Piano hinges are common on teardrop trailers. One issue with a piano hinge is that you need to buy one that has a galvanized pin. The kind found at the hardware stores usually have a plain steel pin which will rust. There are also nylon piano hinges that have no pin at all. The nylon is narrowed in the center to form the bending point.
Gate hinges are another option and can easily be attached without the need for an accommodating jam. These hinges simply bolt on. They also have an advantage over the previous two in that the pivot of the hinge can easily be offset or mounted away from the edge of the door. However, one issue with gate hinges is that you need to find ones with nylon bushings. Ones without nylon bushings are too sloppy to hold the door in a precise position for closing.
Door design considerations
- If you have a square door you have the option of constructing it just like the door of your house, with a home style door jam, seals and door knob. The downside is that its square and not very stylish, however, some clever builders will attach a perimeter moulding around the outside of the door and arch the moulding to beautify the profile.
- One popular door style is the side arch style. It is mounted with a piano hinge on the straight side from top to bottom. Then a seal is placed in the pinch area behind the hinge and a perimeter moulding is attached either around the rest of the outside of the door perimeter or around the complete inside door opening parameter as a seal seat.
- The other styles of doors can increase complexity quite a bit. Basically any door style that does not have a straight edge all the way from the top of the door to bottom of the door on the hinge side is problematic. The reason is that the seal surface behind the hinge mechanically creates a "pitch" motion where as the surface around the rest of the perimeter simply contacts the surface. So for example if you have rounded corners then you have a situation where the motion of the closing door actually traverses the surface sideways on the seal and will tend to push the seal out of position.
It is also helpful to understand how rain will behave on the trailer. Rain will hit the body of the trailer first and travel along the body surface. Driving down the road at 70 mph sets up hurricane force wind conditions. No seals are designed to operate under those conditions. If you look at door and trunk seals on a car you will see that the solution involves designing a channel for the main stream of water to flow around the door harmlessly and use the seal only to stop any extraneous water streams.
So the rules are to design so that openings are flush with the sides and to keep seals out of the main stream of water flow as much as possible. This means if you have an exterior perimeter moulding on the door you may need to have a perimeter "guard" on the body adjacent to the door. Some builders will just put a deflector over the top of the door and down the front.
Its also important to put things into perspective. How much time and effort are you going to put into trying to make the doors absolutely watertight? Its your decision depending on how much effort and money you are putting into the rest of the trailer. However it may be reasonable to consider the home-made teardrop trailer for what it is - one step up from tent camping and thus you really should treat it like a tent. Meaning that after a camping trip, just like a tent, you better clean it out, open it up, and make sure its clean and dry before you pack it away. And if you need to use a towel to catch a few drops while on vacation - don't sweat it.
Our Simple Teardrop
For our simple teardrop the profile attaches perpendicular to the bed. We are also using .75 inch cabinet grade plywood for our sidewalls. Lay the plywood down on the saw horses and draw out your profile and door opening.
You can make compasses by simply cutting a long strip of wood, drilling a hole in one end snug enough to hold a pencil firmly and putting a drywall screw through the other end at the right radius.
The author's teardrop used a 20 inch radius for the front and a 38 inch radius for the rear. The radius for the door corners is 6 inches.
Do not use a radius smaller than 20 inches. In fact, for the front you should choose a larger radius (25 or even 30 inches). The reason is that the top will be covered with 5.2mm luan (birch plywood) and the 20 inch radius required that the screws be started and rotationally and incrementally tightened in order to avoid breaking the plywood. A larger radius will help you avoid this headache.
Once you have your doors and profile drawn, you can start cutting. Use a decent saber saw with a new blade stand comfortably, wear your safety glasses and take your time. The wood cut out for the door opening is used for the door, so you don't want to drill a hole to start the cut. The saber saw cut can be started by angling the saw up, turning the saw on, and very slowly and carefully lower it onto the cutting line you have drawn. Practice on a scrap piece to get a feel for it. After cutting, sand the edges of the plywood.