Aluminum Trailer and General Construction Considerations

Shorty built her tiny house on a aluminum trailer since she was planning on using it to attend many festivals and events. I followed her lead, even though she said she probably wouldn't have done it again.  Aluminum utility trailers are unique and more expensive.  I approached the same guy who built hers and he declined a second chance.  My assumption is that he may have lost money or at best broke even since her trailer was indeed custom.  My search which has taken several months landed me back on I75 North in Ocala.  After providing specs and making minor changes (per Dee Williams' trailer design), I ordered my trailer.  And given its simplicity, the trailer should be done in June.  It should be noted that Dee specs the ribs on the trailer to be welded on the bottom of the farme instead of 2.5 inches from the top of the frame where 2x6 decking would typically reside.  The idea is that you can better insulate the floor.  My last change was to add an utility box made of aluminum on the tongue of the trailer and I squared off the wheel wells.

Weight is the focus.  I expect this trailer to weigh about 2/3 pounds as it's steel counterpart...roughly 500 lbs.  I want a single axle and will use the last 2' as the deck, similar to Jay Shafer's Tumbleweed designs. The cost of my 7x12' trailer will be roughly $3000.  

The owner of Texas Trailers in No. Gainesville at least was willing to bid on the trailer.  They CAN build aluminum trailers, they just don't do it often.  The bid was higher and I'm more confident in ATP's capability since aluminum trailers are their main business.

No one will believe the number of hours of research required. I need a waterproof/resistant bottom and research about plywood and alternatives.  Did you know that a 3/4" 4'x8' ply is 60 lbs?  For my current design, this would mean 500 lbs in plywood.  That sent me back to the drawing board to look for lighter construction techniques...and I'm considering a aluminum frame instead of wood studs. Now finding a aluminum welder that is local is the current challenge (see http://tinyhouseblog.com/tiny-house-concept/towable-gypsy-wagon/ for an example frame.  This is a steel frame made of 3/4" square tube.)  I had decided to use cedar -- a very light wood but having seen what this guy did with 1/4" ply makes me consider that alternative. Perhaps a light colored transparent cedar stain would be as durable and attractive.  Anyway, Cedar needs to breath more than most siding choices and there is a 16 page document on how to install cedar siding (http://www.realcedar.com/wp-content/uploads/2013/06/installingsiding.pdf). I am exploring the use of interior sheathing on the walls, 2x2 studs and closed cell insulation together to minimize the weight and strength of the walls.  I want insulation to save energy, even though the total space is so small it doubt it makes a huge difference.

I seem to over engineer everything I build.  Did you see my Tiny House Chicken House? I worked hard to make it light weight (it is movable)...and I still can barley pull it by hand.  Could there be some deep psychological issue?