First, trailer tires don't get appreciable wear unless there is an alignment problem - and it sounds like you have one. So check that out first.
Second, the problem with trailer tires is multi-leveled.
1) Some trailer manufacturers underestimate the actual load on the tires.
2) Some trailer manufacturers select tires that are marginal for load carrying capacity.
3) Some trailer owners don't follow the speed restrictions.
4) Some trailer tire manufacturers don't produced high quality tires.
These combinations of things cause quite a bit of a kerfuddle within the RV community - and many folks have staked out territory as to what to do about it. Do a search to see the threads where this is discussed.
Plus look below and you'll see others chime in with their particular line of thought. Since I have the floor, I'll start.
First, weight the trailer - fully loaded and tire by tire if you can. If you can't weigh each tire individually, you will need to account for side to side and front to rear load variation. Then adjust the loads for the speeds you tow at. I recommend selecting tires such that they are loaded to no more than 85% of their rated capacity.