Earlier quoted context omitted.
I've already done the rough math. It'd use a Northern Tool 5x8 trailer that costs $550 or less on sale. The $1000 price point is for a basic box to sleep in and store possessions. There would be additional plans for larger builds and more amenities for people with a larger budget. No welding necessary, only basic wood construction.
That northern tools trailer is rated for 1000lbs - you won't be able to have 2 humans inside without breaking something.
You aren't likely to be driving about with 2 people in the trailer.