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From my experience the weight of the skis is unnoticeable but the surface area of the base could be critical. I watch the guys fish Cascade and that snow is brutal. IMHO the flotation would be the key factor in a Smitty up there. Are you going to put a tub on top or just the rails with lashing?
Just found these two videos this morning.Sounds like what you are trying to design. First shows how its built, second is using it.Maybe help with ideas.
While going smaller can work, but it's more about what you put in it, empty my sled with jet sled in it, I can lift with one arm. All aluminum. No so much the homemade as I don't have the skills or tools but maybe you do?
One lake I've fished several guys made sled out of galvanized conduit it seemed to cut though deep 8"-12" of snow easily they'd load their huts gear and auger pushing it or pulling it didn't seem to make much of a difference
I did the same with an old shanty of mine. Conduit runners with UHMW bars attached to the bottom. Worked real nice.