Teardrops n Tiny Travel Trailers

I've been thinking about test driving the TD for a while in polyurethane sealer, before applying the aluminum. Is there a combination of glue and sealer that are compatible? Is flexible rubber trim sufficient to secure the aluminum, or must I bend some more angle? I bought a sheet of 1/4" birch ply for the hatch cover, but it doesn't seem quite "bendy" enough. What glue should I use if I end up laminating 1/8" material?

Thanks for your advice.