I don't think sccachallenger was saying $8900 was low cost, but you were pitched a low cost (4K) trailer with the fact you need more $ to upgrade it and way to much $. It is a shame they are asking that much over there. I have About $5500 total with upgrades in mine and yes the outer sides are paneled, the roof is one piece and the correct 75 MPH radial tires on 5200 lb axles with spare included. I got to see some bones, good or bad! I fixed the bad easily! I was able to fit the car as needed first then trim it out. The unit I got has plenty of frame room for load levelers but my Dually RAM don't need them. If you want a mounted generator you need to consider that it needs to be outside for your safety. I think we are all trying to give you good advice to consider. My trailer as delivered only had a 4' strip in the center of the roof line with 2 LED light fixtures and one vent. No issue to me, the sides were fully paneled floor to ceiling. I primed, painted, carpeted 1/2 way including wheel wells. Caulked all the floor to wall seams first, ( a whole case) and know I have a nice sealed unit that way. Added faux vinyl diamond plate flooring and E-Track, straps included. I over winter the car in it with a 5 gallon bucket of charcoal no issues!
You have to find your comfort zone in price and work from there.
Wow, yours came out great!