2.  Ventilation.  Obvious reasons.
3.  Solid EASY to use Hitch.  Seems the newer trailers have 2 5/16" ball.
The old ones have 2".  I do like the "clam shell type of hitch for bumper
pull.  So far very reliable.
4.  Nationwide uniform wiring code.  Heavy duty wire, heavy duty plugs,
consistent wiring, so if I want to buy an out of area trailer, I don't have
to worry about my brakes fireing when I turn on the running lights, etc, etc.
5.  Fiberglass roofing seems to be working well here in the west.  Cool (
much more of a problem than staying warm. )  Also doesn't rust.  
6.  Lets get some research going on the best rust protection!  Seems to be
the single biggest problem for all.
7.  I like the swing out saddle rack in a front tack area.  I don't have to
crawl in with a heavy saddle after a long ride!
8.  Built in bucket holders and outside hay racks!  So what horse doesn't
need this even at a day show!
9.  Built in water tank ( even 25-30 gal would be greatly appreciated!)
10.  Rack on top for bales or etc.
11.  Light weight!
Well, this is all I have on my list just now, this would be for my "basic"
model.  Maybe I should get into this full time, I know what I like, and what
would sell!!!
Anyone want to place an order <vbg>
Becky Hackworth