Is there a glue that will stick between the EPDM and aluminum?
....always thinking cost/durability, this is what I would do if I were to build a steel-caged truck camper:
-simply paint brush coat all my steel framing with elastomeric-acrylic rubber coating (a kind of super EPDM) rather than a whole-cage EPDM membrane;
-rivet the aluminum sheeting to the EPDM coated exterior cage, using the elastomeric-acrylic rubber coating as a mult barrier;
-affix cedar frame stays to the coated steel cage as a)framework for in-wall wire runs and AC/DC wall outlets and lighting; b) framework for finished RV wall paneling;
-have an accredited foam applicator spray the equivalent steel stock thickness (1 inch ?) of E-84 Class 1 fire rated spray foam to the entire inside cage/shell, thereby permanently locking the aluminum skin and rib-cage and cedar wall/ceiling framing stays (I would personally only use Eastern white cedar, rather than the cheap inferior western red cedar);
-do wiring and electrical fixtures, and install windows and roof vents, then add inside RV wall paneling & trim & bamboo flooring over closed-cell underlayment flooring foam (all over marine-varnished marine plywood sub-floor).
*I would kill many issues this way: absolutely rock solid skin-to-cage composite structure; superb insulation, with fire mitigating foam along with excellent sound barrier (STM yet to be calculted: Standard Test Method airborne sound transmission level); virtually no chance of EVER developing a water (or, air(!) leak); elimination of inside condensation (cedar/foam acting as thermal barrier to a degree); and most importantly: speed of build is accelerated.
