OK here's an almost 1 year update.
DO NOT USE CHEAP LUAN! USE 1 OR 2 LAYERS OF THIN MARINE PLYWOOD FOR THE ROOF! Here's why:
camper sat in back yard uncovered all winter. the exterior plywood held up well. the luan held up where it was FULLY covered. that means that at the bottom edges, water dripped along and migrated up and destroyed it to the consistency of cardboard along the front and back edges.
The Luan is only on the roof part. sides and bottom are 5/8 plywood. all is covered by glued canvas tarp and that was painted with exterior paint and that held up really well. Not a DROP got into the camper even in my home made wood door design. Not a drop. JUST the bottom edge at each end where the water backed up a couple inches and soaked into the luan.
those were caulked and painted but to no avail.
I SHOULD HAVE USED MARINE PLYWOOD.
so today i bought some marine wood restorer epoxy and waiting for the edges I opened to the atmosphere to dry out so I can TRY this $48 dollar miracle juice.
Picture shown is the two layers of luan, with painted canvas. I may have to cut off all the luan and apply marine plywood, but this is just an issue on the bottom two inches at each end so maybe the epoxy will make it "marine plywood" just where it needs to be. I will soak it through and then bolt a stout angle iron across to squish it all together until it cures.
IMG_20170620_195813 by
Chris P, on Flickr