Although much too late - just read this now: How about....

The Missus and I went to the Imperial War Museum(London) last w/end. Arctic/Eastern Front troops sometimes used canoes as load transport - to slide across the surface.
Lets say maybe a plastic (cheap) canoe/Kayak on a rope. Able to cross most terrains. Can be pulled on the rope or pushed/levered if need be. Low centre of gravity for the load(inside) and in the case of an enclosed canoe/kayak.... waterproof.

If it's not a ridiculous idea, it might have some consideration were this to arise again

Martin