"The RV manufacturers get the stuff dirt cheap. A lot actually roll their own."
You know this HOW? I have NEVER seen any RV maker that had their own aluminum plant to "roll" their own Metal siding. The OP seems to have an 18 year old Trailer. Which means it is worth--ZERO dollars. Especially with Hail damage. He needs to live with it unless it leaks from the dents. Years ago they tried to use fiberglass MESA siding on some RV's as a test. Bad mistake. The Fiberglass had waves in it between the studs. Then they realized you had to have a flat wood surface and glue the fiberglass to the wood. Which meant flat fiberglass, no mesa. The only realistic choice the OP has is to buy Metal mesa panels(same gauge) and rehang the sidewall metal. Trying to go larger(thicker) with other material will cause problems with the windows and doors and corner edge moldings that will not fit correctly. Doug