I have the same problem when I load my motorcycle into the back
of my truck. As you say any sloping ground is better than totally
flat. I always look around as I'm driving into the camp ground
hoping to spot something more favorable than just flat road
in front of my site. Usually there is something. I can understand
that towing a trailer and trying to maneuver into a shallow ditch
somewhere is not as easy as me backing my truck into the same
thing. I once forgot to let the air out of my air bags when I was
unloading and it's --really-- steep coming down the ramp with
the back end of the truck up in the air
As far as modification to your trailer, I'm stumped.