Keith,
I faced the same dilemma when I got my Sprint Trailer in 2010. Having looked around, the best I could find was pretty expensive and those I could afford looked a little insubstantial. So I built my own.
Now, at Stewpot we think we've solved the weight problem through careful selection of materials. The Finch trailer is 2.4m by 1.2m (massive!!!) but the weight was saved by using Soffit Board (white uPVC) panels for the ends and sides. They double-up their boats and the size is needed to carry two-boats-worth of kit. My 2.4m by 0.6m version makes more economic use of materials but is still pretty big (sleeps one comfortably!)
The project is pretty straight forward.
- Take a single OSB3 sheet, remove 40mm from the end (bring down to 2400mm) and rip it down the middle length ways. One piece will be the bottom. The second piece will be the top.
- Take the top piece and cut into 3 pieces 500mm, 1300mm, 600mm. The 500mm piece will be fixed to the frame to stabilise the box, the 1300mm will be the main door, the 600mm pice a flap at the end to allow quick access to the box.
- Make a 2 ladder frames 2400mm x 310mm high from pressure treated timber. Screw and Glue the butt joints. Don't faff about with lap-joints or mortice/tennon/finger joints - long screws are plenty strong enough. A 'noggin' piece needs to be placed 1150mm from one end so that it will be 1/2 way along the main door. You'll screw the (hasp &) staple to this to secure the box.
- Screw the ladder frames to the bottom piece. Use moisture curing glue in the joint. Attach cross pieces across the width the box. Attach the fixed piece to the top and you should have a pretty stable frame. At this stage treat your timber with a high-wax fence treatment. Several coats will ensure a decent finish.
- Soffit board comes in 2440mm by 300mm pieces. Cut and attach to the sides and ends. There's a bit of waste here. The board is tongue and grove. Tongue at the top, grove at the bottom. Get the soffit board from a roofing merchant and not from your DIY shed. Wickes charge around 13 quid. The cheapest I got it was £6.
- Use T hinges to attach the lid (15" hinges for the main door, 8" hinges for the flap) and use bolts & nuts, backed off with penny washers. Hasp and Staple on the side and ends
.
- Make a vinyl cover for the top. This is pretty simple. Use contact adhesive to make the hems and eylets to effectively rivet the corners.
The whole project cost around £120 and is pretty straightforward as that it's all screwed/glued butt joints. Attaching the box to the trailer frame was achieved by first bolting some 4x2 bearers to the frame and then screwing the box to these. The bearers allow the box to be attached to more of the trailer.
The white uPVC soffit board gives a really professional finish in my view and reduces the weight by around 50% compared to Marine Ply. OSB3 is fully waterproof, lighter, simple to work and much cheaper than ply. Treated, it should last just as long.
Regards
Karl Pountney.