The hatch lid has to hold its shape. According to various sources I've read on the web, and in the plans I have, earlier lids could tend to straighten or lose their curve, or in some way be unstable. I did not want to frame my lid from plywood. Plywood's greatest benefit is delivered in sheets rather than narrow strips or bands, and I think it tends to be a bit heavier than ordinary pine, per square inch. I used clear pine, and cut my curves on a bandsaw. I also used pine for ribs, and made the ribs wider in the area where my tail lights would be. The outside surface of my lid is sheathed in 1/4" plywood. Since the lid is about 5 feet long, I decided to use a single piece of plywood with its outer grain running lengthwise . There would be no seams, and the usage was more economical... though probably only in my mind. The problem with bending the plywood on this long axis, is the the plywood is more stiff in this direction and will act to straighten the lid. It certainly did act to cause the lid to bulge outwards slightly on its bottom edge, which will complicate the bottom seal project.

I do have what I consider to be a very sturdy lid, and I do not think it overly heavy. At this writing it is not finished on its inside. I have more work to do in the galley, and not yet decided on just exactly what it will look like. I'm working out the arrangement and details, now. I really want a serviceable galley for our trip in April, even if the trailer is not completely done by then.

the basic framework - ribs are 1 1/2" deep and 8" apart - the 2 lowest ribs are 2" deep and there is a trasition rib 1 3/4" deep above them - the sides are cut from clear 1x8 pine

this shows the detail at the lower edge of the roof lid

using a piece of paneling to derive a fair curve between the ribs, for nailing strips for the interior lid paneling - a piece of nailing strip is laid in place behind the paneling, and the curve is traced onto the nailer for cutting on the bandsaw

nailing strips nailed and glued into place

I fastened the lid frame in place temporarily and then screwed the outer plywood skin to the frame - the plywood is securely held in place top and bottom with 2x4s and rope and ratchet straps until all the screws are in - note that the outer plywood grain is running lengthwise - when the ropes and restraints were released, the lid kept its curve

I made a form for the exact (as close as I could get it) shape of the hatch lid - this would have to be very accurate so it would not tend to want to straighten the lid - this molding had to also be flat in the plane of the plywood form when it was released from the clamps. This was a fairly robust piece of molding and I annealed it twice. It was cut from 2" x 2" x 1/8" angle, and I ripped one edge of it to 1 1/2" using my bandsaw on its slowest speed. The cutting turned out very nice, with no attention-getting moments. I have a perception problem that kicks in at odd moments, and so I had to pay particular attention on bending the second molding to make sure I had a true mirror image of the first, instead of a copy of it.

I use various bits of scrap wood for pounding blocks when shaping aluminum. This kind of pounding block should actually have been about one inch longer, one time. A bit of skin at the base of my forefinger got sorta folded over the top edge of the block once. There is a reasonable limit to how cheap you can be. Use a bit longer block.

This is out of sequence, here, and just shows the holes for the tail light wiring in the lid.

Setting the lid frame in place, you can see the holes line up with the holes in the roof edge.

first page the frame the floor the sides the roof the flooring the shell wiring and insulation sheet metal molding the hatch lid doors fenders light fixtures cabin cabinets solar panel tanks other stuff