I'd chock wheels on both sides of the trailer, disconnect from the tow vehicle, and level it. If you see the site is really out of level, you could back the trailer onto blocks so you don't have to jack it so high to level it.
If your trailer has dual axles, the locking chocks that go between the wheels and lock both wheels from rolling would be a good idea, but I'd still use wedges on both sides of the tires.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI