We just purchased our first enclosed trailer (very low budget) is 64” tall inside (68” peak has slight pitch to roof) total box length is 13’ and has an 80” v nose 8’ wide inside. As you can see barely enough room for 2-144’s and 1 155” (could probably for three 165’s of newer style sleds as they stagger a lot better) could get away with a 7’6” wide if you have new sleds with narrow front ends as a stock mtn sled is 43” wide or 7’2” wide (2 wide in trailer) might be able to get away with a 7’6” W 18’ L if it has a 18”-24”+ v nose loading all from front into rear facing the same way.
Trailers are selling for a premium this year used. If willing to travel you can get a brand new one in the Midwest (Chicago land area) for cheaper than used ones out west. 15-40% cheaper depending.
Get some 2x4s and layout your three sleds then create a 8’ wide trailer vs 7’6” and see how long/wide of a trailer you would need. Yes you can just lay them out and measure but using the 2x4s to make a structure realllly helps put the size of trailer needed into perspective.
Good luck and happy sledding!
Ps our 64” ceiling is not as annoying as expected