You can get two in that 6x12 ???
He said
"We could fit (2) 155” sleds in it". So there you go. I assume that was loading one backwards and them practically touching. I doubt two 165 would fit, and it might even depend on the model of 155 that fit.
Our first enclosed trailer was a beat up used one that we had to back one sled into to get them to fit. Worked for a time but was a pain. Showed me we really valued an enclosed trailer, though, which was the intent, so after a year, we sold it and bought something nicer, but bought a 7' x 16' so we could load two long track sleds without backing in. Also could fit two ATV end to end. Still own that trailer today. But I digress from the original posters "single sled trailer" question. For that, any enclosed trailer will do.
Not sure if enclosed was the intent, but enclosed is highly recommended over an open trailer. Pros of enclosed are, security, out of the weather, not deal with road grime, a place to change clothes, a place to store the sled or other items to free up garage space, and protection from critters. The last open-trailer straw for us was 10 - 20 crows picking holes in our sled covers and sled seats when parked in West during the classroom part of an avy class. Idiots parked next to us stood out there during lunch eating pizza and threw every all of their crust on the ground. A murder of crows descended and picked holes in everything with a 4 vehicle radius of their rig including both of our sled covers and through the seat on one sled. Fun. The idiots, of course, had an enclosed trailer so no damage to anything of theirs. When we got home from that weekend, besides finding seat repair kit and patching holes in sled covers, my enclosed trailer shopping started and we had one within two weeks.