Lift kits
And then some of us raise them even more -- the bottom of the walls of my trailer are two feet off the ground, after we flipped the axle! The only limitation on ground clearance is the distance between the ground and the axle, which is about 10 inches, the same as my truck. Steep driveways are not a problem. But big rocks in the middle of a dirt road still require some careful driving.
And yes, the lift kit means a higher center of gravity and more wind resistance. Life is a series of compromises -- in order to go off road (slowly and carefully), we had to lift the trailer.