If 18 you should be fine, but you need down slope for drain.
If you know where the utilities area you could consider removing some dirt to make a bridge area above them, dumpa couple sacks of concrete and set it down, mix in place and level with a 2 x 4, toss some rebar if you have it, only needs to be couple inches thick and below your base.
This will insure load is spread out to avoid compression.
Tony & Lori
1989 Country Coach Savannah SE