I have found that if you step back 20-30 feet from the trailer (both at the side and at either the front or the rear) you can eyeball the level closely enough that you won't have any problems. Try it, and then check it with your level. You might be surprised at how well you can do. However, levels do have their place - especially on the mini-lots you find at some campgrounds.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.