fornesto - I used a boat trailer and lowered it by doing a spring under. Originally the axle sat below the springs, I unbolted the axle and placed it above the springs, dropping the trailer about 2.5".
Of course, if by solid axle you mean it doesn't have springs, then either don't use it, or get some springs for it. It would beat your camper to death w/o them.
I'm actually going to remove one of the springs from the spring pack because my camper is so light.
ï¿½veni, vidi, vici.ï¿½