New enclosed trailers are measured outside width, not inside. To get them to EASILY fit side x side you would be best with an 8' or better yet 8.5'.
If your hauling 4 sleds regularly a 7' inline works just fine, and gives you the room to squeeze in a 5th if needed.
Last year I bought a 2015 Ameripro 7x29, I hauled 5 long track sleds (155, 153, 154, 154, 154) in it every weekend with no problems. See the first picture. With that trailer I learned the hard way that you get what you pay for and it didn't last a year of normal use.
I now own a new Aluma 8.5x28 (24+4v) lowboy car hauler, twice the price, but 10x the trailer and worth every penny. I will never go back to a 7'. This trailer while being heavier pulls so much better, doesn't sway, and while being a foot shorter total, has tons more room inside. Definatley the 8.5' lowboy car hauler is the way to go. I can very easily get 6 long track sleds inside.
Having the sleds side by side is extremely easy to get around, I would typically cram 4-5 long track sleds into the 7' and what a pain to get around and tie down..
Here are some photos of mine. It is a 2016 Aluma 8.5' x 24' with a 4' v-front. 100% all aluminum, no wood. All aluminum floor and ramps. 5200# axles.