Today I got the 1/4" sanded ply for the headliner. I am a bit frustrated it did crack in one spot. I glued it all and used brad nails to secure it until dry. The good news about the crack location is it is actually inside one of the cabinets I am building in the interior.
Looking really good so far! I know those cracks can be very discouraging. It happened to mine on my first build but i was able to sand it down and fill it and paint it, you couldn't even tell it was there after.
You could glue a piece of plywood to the back side to strengthen and get the correct curve .... Screw a piece of wood across the ribs with a brace between the wood and the added piece until it dries ....then remove the brace and the wood.
I currently have a home made steaming tent running in the garage. It involves saw horses, a tarp, some styrofoam insualtion, 2 pots of water, and a camp stove. Pics to follow.
Some of the steaming guides I have seen said 1 hour of steam per inch of wood so i'm guessing 15-20 minutes for this 1/4" piece.
I have ran wires, test mounted the hatch, insulated the voids, and put the 1/4" AC ply on the outside. Now I need to get my aluminum skin so I can keep this project going.
Lookin good! One thing you might want to consider on your spars. I set my spars into the plywood, meaning i cut a slot in the edge of the walls to fit the spars into. I only used three for the whole roof. Insetting them gives them more purchase, meaning there is more surface area of the spar contacting the wall thereby giving more strength. The strength of your joints is limited to sheer strength of the screws. If you changed out three maximum the strength would be increased a lot. Something to think about before the roof goes on.
I am a bit late to this party, but just thought I would mention that I ran a wallpaper steamer inside my cabin while I was fitting my interior curved ply and it worked a treat.