Supposedly, the 5er would have fit in the third bay if it didn't have the 3" lift and the front roof vent. We were able to easily remove 1.5" of the lift, but still too tight at the front, so like any well mannered trailer, we taught it to kneel. A couple of the half-sized piano dollys from Harbor Freight, a modified crank, and away we go. We even got lucky with a seam in the driveway in just the right spot for raising it to hitch height.
I set it on a jack stand once it's inside so there isn't any significant load on the dolly wheels except when its moving.