If you are looking for things to last there are solid oil bearings (or whatever they call them) that have the bearings encased in a oil filed polymer which might work or ceramic bearings could work there are certainly plenty of things that use bearings under water. SKF and NSK make solid oil bearings and stuff for underwater I would reach out to them once you have sizing and see what is possible. If just using it once then yeah what
dedhed said will keep you enough out of the red and if you put some big bags on your sled they might call you a Fred just make sure they are waterproof or they will sink you instead.