If you are still considering the winch idea and think that there isn't enough room for it between the wall and the trailer remember that you could bolt it to the floor and hook the winch line farther under the trailer like closer to the axle and then when the trailer got to the back of the garage the trailer could go over the winch and the winch could still have line left to pull since it would not have bottomed out yet.
The harbor freight winches for the weight you need wouldn't be very expensive and this might be the best idea. You could then raise the "JACK" with the caster wheel as high as you need to get the nose up and the back down so you would be able to clear the garage opening without having to manually pick up on the nose of the trailer, but you may have to crank it back down to level the trailer once in the garage to clear the winch bolted to the ground before you got to the back wall.
