I have a Sundowner 3 horse slant that I haul everything in - big horses & minis - so I can't have permanently installed mini dividers. I started working on dividers last year and found them to be pretty expensive. The pvc gates are an interesting approach, may look into that but I would have to configure without the permanent posts in the middle of the trailer. It may take more room, but I personally like having the dividers at a slant. It makes walking the horses in and out much easier, especially with a taller horse, if you don't have a sharp angle to turn them into. The ones I have used also don't go all the way side to side, so you always have an aisle to walk behind & access horses without unloading.
What I do like....height of the trailer, have had a shorter mini trailer (could stand in it but had to duck going in the door...lots of headaches lol), love having a ramp and a trailer cam. Great peace of mind to be able to check on your horses going down the road, especially on a long haul.
The shorter trailer we used for awhile had a rack on top, but I found for me, it was a major pain to haul carts up to the roof. I had to either rely on my daughter who was pretty small at the time, or hunt for help at every show. I had rings installed in the roof of the Sundowner so I can pulley it up inside and haul it alongside the ceiling if I don't have room to stand it in the rear.
Jan