We were out there last year in Aug in a stock Rubicon 4 door. I didn't see any trails that would be hard with a trailer if you took your time. There was one off camber down hill 180 turn just past California Pass that had a little pucker factor. But I wasn't feeling the greatest that morning and I think that didn't help. The biggest factor will be other drivers. Most don't know the uphill driver has the right of way. RZR's think they allway have right of way. We had one spot on Corkscrew we were heading down hill and came nose to nose with a RAM 1500 four door 8' bed. I had to backup well over a mile to where he could get by. Would not be fun with a trailer of any kind. If it were a jeep or something smaller there were many more places the pass could have been made.
We camped very near Animas Forks, had a great spot. Quite on Thursday night, Friday evening was heavy traffic till just past dark. We are early people so we were on the Engineer Pass road by 6:00 didn't see anyone to well after 10:00. Afternoon was a little busy but not bad by the time we got back to Animas Forks and our camp it was crazy busy 3:00-4:00. We walked from our camp to the old town. I was asked two times what is the fastest way back to Lake City. They had rented jeeps that needed to be back by 5:30-6:00. The one guy understood he was screwed, I told him I thought Engineer would be quickest at 3-3.5 hours. The second guy was convinced that taking pavement would be faster. I wonder what his overage was. But that is what you have to deal with out there. people that have no clue about mountains, driving off road, Being prepared for the weather. The pavement guy had a jeep with no top or doors, t-shirt, shorts and flip-flops. I bet they had a cold ride once the sun went down.
We will probably go in August again this year. I hope to have my teardrop camper done for next year and will go in September for the colors. Tent camping in August at 9500' is at my wife's cold limit. We had one night at 29 degrees.