What’s your budget? What’s your tow vehicle?   7 x 18 with 5’ Vee or 23 length is smallest I would go.  We load a ZR 9000  137”, Polaris Assault 146”, and a skidoo 900 turbo renegade and there is a little space left for gear.  I wouldn’t go smaller.   Depending n your budget and needs Speedway Trailers has a nice looking Alcolm trailers hybrid 7.5’ x 22’ .        

Mine is 21 ft including V. 3 . 144 sleds and it's full.. Best to drive in v door or back in for 3. Works for me..

Funny this is asked.  I actually was asking this same question earlier this week and did a layout on the garage floor with chalk lines.  Scottyr is 100% correct.  With 2 - 137” skids and 1 - 129” skid all trail width front ends I found a 7’ x 18’ with a 5’ v-nose was the smallest I could make things fit in.  7’6” width does make things fit easier, but I wasn’t convinced it would get you into a 16’ trailer.  Question to ask is what is the actual interior dimensions of a 7’ x 18’.  If it’s a Triton PR187 then the interior is only 80.5” wide.  You loose 3.5” for the walls.  I settled that that trailer or one of equivalent size is what you need for 3 sleds.  The PR147 (14’) and PR167 (16’) are two place units.  When I looked at total length the PR187 is quite comparable to the size of an 18’ bow rider boat on a trailer.  Manageable, but still long especially if you have cottage roads to contend with.  There is so many times that spinning the 2 place clamshell around in a tight area is super easy.  I do agree getting away from the 102” width is a good plan for visibility and aerodynamics.  You want the narrower width and the lower ground height to cut down on drag.  If you think you could ever own 146” or 154” sleds you might want to go to a 20’ unit.     Anyone have experience with Beckner trailers?  Look to be a decent build.  Possibly comparable to Triton, but a touch of a no frills setup (not the same options for the floors, etc.).  Canadian made too which is attractive.

If you can find a 7.5’ wide vs a 7’ wide.  7.5’ isn’t as common but it is surprising how much more room it provides. 

From experience 7 x 18 + 4/5ft V is the smallest you can put 3 sleds in comfortably.