I was trying to figure out how they were built. I was assuming they would all be the same, but some were unfinished. Now that I know they are supposed to be different it all makes sense. I like the look of the tray ceiling. It's a clever way to get more head room without taller walls. Are there any limits on the stregth of tray ceiling trusses?
nice home! As for regisering it, not sure how it works for you in your state, but here we just fill out a form for a homemade trailer, take it to the nearest truck scale and get a scale ticket and go back to DMV and complete the registration. Since your trailer wasa mobile home before, you should already have a vin number, if not just get a new one issued from DMV when registering.
The top triangle is a truss, so it is primarily limited by the 2x4 span, which is ~3 feet on a side. The supporting joist section is a 2x6, and is less than 2' long. The total span is a little under 8', so there is basically no problem with any type of loading. As it is with the truss structures I designed, you could land a helicopter on the roof if you wanted to.