Dave's post finally triggered the light
bulb to go on over my head... this loading requirement is only at home. That opens up all sorts of options for equipment (some already suggested) which would not be practical to take along on the trip, but might belong in a home garage.
A common shop crane
(wheel-mounted, using a manual hydraulic cylinder) is normally used for tasks such as engine removal and installation, costs a couple hundred dollars, and could easily put the generator in and out of a truck backed into the garage.
I have a chain hoist
hanging from a ceiling beam, which I have used for engine swaps (instead of renting a shop crane, because I don't own one of those yet). It would be easy to lift the generator, back the truck under it, and lower the generator into the box (and the reverse upon return).