Mark paid $500 for his Avion T-20 in Tennessee not too long ago. Says internet: “The body of the AVION Travel Trailer is two complete Aluminum shells one inside the other, separated by a blanket of 1 1/4” plastic treated fibreglas insulation, riveted together as one unit on aluminum stretch formed bows and stringers. The only wood used in the construction of the AVION is the plywood floor and cabinets.”  Brochure here, and 1963 price list here.  I estimate that this 20′ Tourist model trailer cost new about $4k, weighing roughly 2600 lbs.