Slim,
Before going to a whole lot of trouble, go back to basics and check the 
simple things. First, make sure tire pressure is equal in both tires and that both 
tires are of the same make and size (yes, size matters). Second, make sure you 
don't have a bent rim. Jack each wheel up and spin as much as possible and 
check for roundness or any possible wobble. Thirdly, check to make sure the axle 
is mounted square on the trailer. Measure from the center of each hub to an 
equal point on the front of the trailer. Even a 1/8" difference will set up the 
wobbles.
Different makes of tires, such as a Goodyear on one side and a Firestone on 
the other side is a no no. Although rated the same, size and weight etc, each 
tire will turn a different number of revolutions per mile (check manufacturers 
specs if you don't believe me). Balance is key to resolving this issue.

Rummy