Camber would not cause wear that fast unless it was ridiculous, and you would know what the problem was because the wheels would be tilted in so far at the top it would look funny. I've run 3+ degrees of camber on some cars I have, which is very noticable, and it gives very little camber wear in the inside of the tires.
Toe, however, can easily scrub away tires in no time. If they are worn on the inside of both tires, they have a toe out condition, when looked at from above, they would look like this " / \ " with forward being the bottom of the screen. The tires are trying to turn away from each other while being dragged forward.
I would imagine that you experience some instability in the trailer with a setup like this, does the trailer wag?
I would imagine the only way to fix this on a beam axle trailer would be to bend the axle back into shape. Right now it is probably bent with an arc going toward the front of the trailer. Measure the distance of the axle from a know fixed point that is not part of the trailer, to the left, right, and middle of the axle to see if it is true. If it is bent as I suspect, Try chaining the center of the axle to a big tree and pulling a little with the tow vehicle...but be careful, don't want to pull too far.
Also try measuring for toe angle...
What I do is use a plumb bob and a tape measure. Plumb down one of the trailer tire grooves in the front and mark the ground where it touches. Then do the same thing on the other wheel in the corresponding groove. Measure between the 2 marks to the 1/16". Repeat the process on the back side of the tires. Make sure you use the same grooves in the tires as you are going to compare the measurements. If the measurement on the front is larger than the measurement on the rear, you have toe out.
or ya could just flip the tires inside out and get another 12,000