Fiberglass and aluminum... If you can find a set of wheels from a Cavalcdae or Bushtec trailer you can make an axle, you can buy mini airbags from McMaster carr... all the MC trailer axles will be 500 lbs capacity and will be harsh...Biggest thing will be finding someone who can jig it up for you and weld aluminum properly to stay sound. Really isn't hard to build the shell out of fiberglass... Use cardboard, line it with saran wrap that would be stray glued to the cardboard, start with a layer of resin and fabric, i would use the tiger air type or interweaved type fiber glass fabric. Sand the outside, prime, sand, prime sand and spray paint...You will have to be creative... I have seen some pretty cool looking trailers that were hand built like that behing Motorcycles and some were really light....Ptience, measure twice cut once....