Won't someone please make rugged small trailers??

A Casita or similar will be a good choice. Change to torsion axles.

Longest life will still be all-aluminum. There were some xtra short models built. Last indefinitely. Have them rebuilt the way you want. Avion, Streamline, Silver Streak and least desirable, Airstream.

As in, "my 2012 model year trailer won't last forever", should be first clue about what matters.