Thanks for the comments!
I have been refining the details, mainly how it seals the joints when open, and it's looking good. This design gives the most room with the least complications, and has plenty of storage when closed for items such as a Drifta-style pullout galley.
There will be an awning/tent off the back for more space; the trailer is mainly for secure sleeping quarters and a way to haul "stuff."
Opinions requested on width: wide enough for a sideways queen (7' exterior), a short queen (6'-6" exterior), or put the mattress lengthwise (5'-4" exterior)? I want it to be easy to haul into remote places, but not looking to do any super-hard off-roading with it (pintle hitch stuff).
Trying to keep myself from adding a slideout bed... the extra space it allows is nice, but I'm trying my best to keep it simple.