Why won't the ramp trick work? With a 40" wheelbase, you just need to make the ramps out of a crosstie, which is twice that long. A chainsaw used to cut a ramp about two foot long on one end should give enough slope to not hit the front or drag the middle as you climb the incline, and not give you a problem climbing it with a load. If it is too much of a slope, cut a little longer ramp. I can't see why it won't work, unless there is something you haven't told us, or that you want to be able to place stuff anywhere on the upper level, and don't want to have to move the stuff on the ground floor out of the way to do that. If you just want it up there, and then plan on moving it with a pallet jack, or other means, no problem.
David from jax