When I constructed the skeletons for the front skirts on 'SPIRIT', I used aluminum 'rulers' from HARBOR FREIGHT TOOLS.
They're in the same section of the store as spirit levels.
The material is a couple of inches wide, and thicker than an 1/8th inch.
Also, their spirit levels are cheap enough to use as aluminum I-Beam.
AeroStealth had an APEX RV trailer that he pulled with a 4RUNNER, and I constructed a roof-mounted air deflector, made from a discarded HIGHLANDER rear hatch frame, mounted to 6-foot level I-beam, attached to the 4RUNNER roof rails.
It's the cheapest source of alum, extrusion I've been able to locate.
Only one metal recycling center allows 'salvage', and 'supply' is really hit or miss.
