They can be mounted anywhere that is most convenient for you to use. Screw on is the best way. The stick-on tend to shift when they are exposed to hot, cold, wet, dry. The larger, slightly curved ones seem to work the best.
Meticulously level the trailer then mount the levels.
Chuck - Sparta, TN
2012 Jay Flight 22FB, 2 x Honda EU2000i
2013 GMC Yukon XL Denali AWD
EDUCATION is what you get when you read the fine print.....
EXPERIENCE is what you get when you don't.