I have a bike trailer, with a fairly steep ramp.
I have a plank of wood placed to the side of the bike ramp, and simply walk up it next to the bike, engine running, in gear, and it goes up a treat with no issues, moderating clutch/power as it goes.
Coming back down however, remains an issue if the ramp is wet, because the wheels just lock with the brakes on and it can slide easy. Dry no problem at all, but wet requires some care!