I had a set of these in a load range "C" that seem to do OK.  http://www.easternmarine.com/st225-75r-15-radial-tire-lr-e 

    I ran them in the heat in Florida, through the mountains and on some rough interstate highways, held up fine, always kept them inflated to the maximum pressure..... I replaced them after four years and they were about 80% worn out. Probably had 30K on them. Put Goodyear Marathons back on, we'll see how good they do. Would like to have gone back with 16" wheels, but I only got 5 lug hubs, have yet to find a 5 lug, 16" wheel.... Alot more choices using the 16" wheels, like the fact that you can use a "LT" truck tire instead of a "ST" trailer tire.

Some "ST" tire info....  http://www.discounttire.com/dtcs/infoTrailerTireFacts.dos