Must have - A good weight distribution hitch with built in anti-sway. Plenty to choose from.
Avoid - Trailers where the foot of the bed butts up to a center mounted entertainment pedestal. Your pillow is going to push you to the foot of the bed and your feet will hit the wall. This was bad enough for my kids that they sold and she is 5'-4".
Nice to have - Slide toppers.
Avoid - Ganged automatic stabilizers. Make sure you can lower them separately.
Avoid - There are a lot of different slide mechanisms; Schwintek (?), cable, etc. Some may not be the best so do your research.
Nice to have - Front and rear fiberglass caps.
Avoid - Axles and tires whose capacities bump right up to the trailer's weight. I like a safety margin
Nice to have - Heavy duty entrance steps.
Nice to have - A large gray tank. Black also.
Have fun shopping