Tex,
My Hasty Vac does great on hills and slopes. A large portion of my yard is 15 to 20 degree slopes and I go through those areas with the trailer like it wasn't even on the back of the tractor.
With the trailer units your main concerns are acute turns and then clipping trees when close to the woods. Both those are just seat-time learning curves and watching where you are going.
I've tipped mine over once on it's side, when I was getting a little too close to a drainage ditch and dropped a trailer wheel into it. It came crashing over, but Hasty Vac has already thought of that and they have a 360 degree pivoting hitch so that it does not upset the tractor at all. The trailer just fell over and that was that. Once I realized what happened, I just shut the vac engine off, climbed back on the tractor - engaged the low range and 4WD, then pulled it out on its side to level ground so I could right it.
I did my yard yesterday again, this time all the leaves were dry and the speed to pickup with the 60" Kubota Deck was much better - at a moderate pace - than when the leaves were wet. At 32 bushel capacity, I had (4) loads of leaves on 2 acres. So that's about 130 bushels dumped in the woods. If you get smaller units, at say 12 bushels, you're dumping 10 times!
Go for the largest one you can afford and you'll find they tow real nice and are very easy to hookup.
-Duane C.