I did the same thing to my trailer many years ago, I have a tandem axle 21ft V-nose aluminum construction. With aluminum trailers it will shrink in the cold weather. Its amazing how much it will shrink. I trimmed my inside with luan and cut luan strips for the trimming. In between the wall studs there would be about a 3/16 gap from the wall during the winter and in the summer it was flush against the wood. Just some thoughts. Great job on what you have done so far.
Also run the sled in from the front when loading a ton more room. I can get 3 long tracks in mine that way.