I use a torpedo level as well as stick on levels (to get ball park). I use the torpedo level in the driverside front cargo hatch, since that is where I store all my level blocks, wheel chocks, and hitch tools.
I have noticed that side to side level is affected by putting out the slide.
a friend of mine levels his trailer by using a hydraulic jack between the wheels in lieu of wheel blocks. jack up the side that is low, lower the stabilizers, and enjoy the weekend.
2008 26BHS j-flight II
2010 RAM CCLB 2500
Reese strait-line hitch.
DW, 5 kids, and a dog.