My first thought is that if you are this uncomfortable about doing it, than don't do it.
Most trailers and tow rigs can do much more steeper angles than you'd think.
Having said that... If you go too steep / angled, you may not know it until something bends or breaks.
Also, what about getting out? If it is that steep going in, can you get out?
I have to chuckle, though... friends of ours bought a cabin in Vermont - when they invited us up, our first question was "can we bring our camper?". They said we should probably take a look first. They have over 10 acres, and not 1 spot flat enough for a camper! lol!