i've done a couple hulls on the trailer, or stand, what I do is buff as far down as I can reasonably.... then tilt it on the trailer way left and buff away, then tilt it on the trailer way right, and buff away, that will get 90%. you can also flip it backwards on the trailer and let most of the front of the bottom of the hull hang over the back (just keep the trailer latched to your car/truck) so it doesn't flip backwards, and keep it strapped to the winch. Then I can stick my hand in the hard to reach places, and wet sand any left over spots fairly easy... (or climb underneath, but see below)
you really don't want it laying completely on its side...
i don't recommend laying on your back under the trailer buffing, shit fly's all over your face/shirt, I won't do that again, if anything i'll wet sand down there, but not buff.