I think if I were going to do alot of traveIing I would look into the sprinter vans,I really like the web site link it's given me alot to think about.
after reading your post I found 2 dodge sprinter high top vans on craigs list for sale and alot on ebay, just not sure I want to tackle building one from scratch when there are some nice B class motorhomes for sale ?
BTW I think the drop down room would come in handy I wanted to add a room on to the back of my trailer so I built a 5ft long box out of 2x4's and made it the right height to go under the rear ramp so it's like a little deck,I also made it to hold my gas cans when I am traveling.
I bought one of the vintage awnings but I haven't got around to makeing the screen walls, the only thing I don't like is you have to stake it out with rope on the 2 corners, it's kind of a hassle unless your going to be set up for a few days.