'06 Xpress X19 TS | 150 Yamaha VMAX
I had an issue just like yours although on the outside of the tires. I'd put new tires on and in about 2 years they were worn again. I ended up putting heavier springs on the trailer and went to "D" load range tires on while upgrading to 15" rims and haven't noticed any problems since. I believe it was caused from too much weight and tires bouncing going down the road.