Musky,
The biggest issue with trailering sleds is that on an open trailer the sleds tend to get rusty - so anything you can do to limit that (including sides) is a plus.
We used to trailer our sleds between the SE part of the state and Vilas, but have since decided to just keep them up in Vilas.
My sled in a 2016, with 0 rust. My previous sleds had rusty A-Arms, shocks, etc.
Unless you spray your sled off with water whenever you get to where you're going, rust can be an issue.
I suppose a guy could spray rust prone parts down with something like WD40, but either way it's something to be mindful of.
If I were in the market, I'd look hard at an enclosed trailer. Also, you can keep your sled in the enclosed trailer for cheap at an outdoor storage space in the off season, and keep your sled looking new (and keep the mice away,)
Indoor storage is quite a bit more n than outdoor storage.
Edit: If you do go with an open trailer, the 3 inch sides really help keep your sled skis in place. It's a helpful thing, as sleds can jostle all over the place going down the highway at 70 - so it's a little extra insurance they won't go anywhere...
