I use the level on the electric jack. It has a large round level that checks front to back and side to side all at once. It wasn't correct from factory but it is adjustable so I set it using a 4' level on kitchen floor.
2007 Toyota Tundra Crewmax LTD 4x4 5.7l w/4.3r 381 hp and 401 lb-ft of torque
2012 Jayco 32BHDS
Me, Wife and 3 kiddos