On first camping trip with TT, I took a zillion "readings" from level on floor, counters, tongue, etc. (yes, all were different) - opened/closed cabinets, doors, and fridge door to see how resistant/assisted swing was and got it as level as far as I could.
With it now level, I then installed a side to side level on front of TT - in view from driver's seat while backing in - for side to side and then installed a small level on portion of tongue that runs front to back. Both these levels are now "calibrated" to this "level of levelness."
Now, when setting up, I get it level side to side while backing in with the level attached to the front of the TT -- use beveled 2x8's and/or Lynx Levelers to achieve levelness. Then, after chocking TT wheels and unhitching, I get it level front to back with electric tongue jack using level on tongue is easily viewable from tongue jack.