If you are going thru tires as bad as you state SOMETHING is wrong or damaged on your rig.
Replaced them recently and put Maxxis M8008's on the trailer. Pulled to the Motorplex from around Little Rock, 781 miles give or take (round trip), these look like they're still new. Can't tell there's any wear at all on them. I've seen this many many times...boat, utility, enclosed trailers all of them. There is some real junk out there. Even had this similar issue out of a set of BFG KO's on my truck....got 13,000 miles out of them. BFG (owned by Michelin) was no help. They basically said that there's no treadwear warranty on them. Needless to say, I didn't buy another set. I bought a set of Yokohama's which currently have 61,000 on them and I think there's still another 10-12k left before it's time to replace. No other changes, not even tire pressures.
That is why I mentioned it.
One can check alignment at home, easily. Pull trailer to a flat open parking lot. When you get into the lot, straighten the rig up while driving forward, need to go about 100' or so. Stop. Now grab a nice straight piece of pipe or whatever (I use a piece of square tubing) and lay it across the middle (or above the middle if the center cap is in the way) of front & rear tires. If there's a toe issue, you'll see a gap. String can also be used but I just use the tubing because it's what I have. You can also check the camber with a plumb bob, or like I use, a nice straight 2x4 with a shelf bracket screwed to it. A little camber is fine, up to about 1°. Any more than that and it's gonna wear the tires. Caster is built into the axle and for the most part is nonadjustable.