If it's really bad you may want to bring along a bunch of 2X4s about 24 inches long that you can stack up log cabin style under your tongue jack and stabilizers. Be sure to use the type of wheel chocks that lock between the tires instead of just block the tires.
I've been in sites where I've had to raise the tongue as high as the tongue jack will go and then place blocks under the frame so I could raise the tongue jack up so I could put more blocks under it to get the front of the trailer even higher until level. Then I placed more blocks under the frame to stabilize the trailer. The rear bumper of the TT was nearly touching the ground.
I had to add blocks under the wooden step we normally use to raise it up to make it easier to get into the TT.