[Berger_4_]

Couple things that I'd look for:

Look for a trailer with the fridge and kitchen area right next to the door. It's way more convenient for getting stuff out for meals and such.

Try and find one with a roll-out storage thing...my parent's trailer has this and it's absolutely awesome. You can keep way, way more stuff in them than if you just had doors.

If you can, a bedroom you can stand up in is pretty nice. Way better than crawling around on your hands and knees.

Slide outs, while a bit more money, add a huge amount of space to your trailer. Just make sure they seal well, otherwise you'll get a whole bunch of dust in there.

Dunno if those last two are a possibility in a trailer under 20 feet, but it's worth a look.

Oh and if you can get a fifth wheel...do it. Way easier to pull, and you can hook your boat on behind too (as long as you aren't over a certain length).