Use a regular carpenter level, 3 to 4 ft. Set it on your kitchen drain, the floor or on the Island top if you have one. Back the trailer up to the spot you want, then check your level bubble, if not level then pull forward and then place your leveling blocks on the low side. Start with 1" levelers at a time. repeat the process until trailer is level.
Your second option is a "Level Master with mounting bracket" on the front of your 5th wheel hitch. Each bubble mark represents 1 inch, so you can tell how many levers you have to put under the tires to level the trailer. Camping World has some new levelers that are much wider than the usual small yellow plastic levers. It makes it much easier to back your tires onto the levels.