Aliners are very cramped, even for 2 people. If DW does not like tent camping, I don't think she would like being in such a small "pop up".
If you want to boondoock a bathroom is IMPERATIVE even it is uses a composting toilet.
You will be much happier with electric brakes. Even with brakes, I think your minivan will be "challenged" on long uphill grades.
I have been dreaming and researching about building my own trailer (quite a bit bigger than what you are think of). The most common failure is roof leaks, especially around roof protrusion (A/C or vents). Typical RV "rubber roofing" does not have a long life so aluminum roofing is a good idea. Attaching the roof to the supports will be an issue. Caulk/sealants also do not have a long life. Boaters use butyl rubber tape. Build so that the window/vent/etc can be removed and the butyl replaced.
"Real" marine plywood (BS1088) is very expensive, but a couple coats of primer and a couple coats of marine top side paint and it will last for a long time !