We had the same issue years ago on a steel trailer we had, going down the road to High School rodoes and changing a tire every 100 miles or so, wasn't any fun or cost effective.

We found that our axels were out of alignment with eachother, a few adjustments and never had another flat on that trailer again.

Best bet is to haul it in to your local tire/mechanic shop and have them align everything.

Good luck and Happy Trails..

I hit something on the road and bent my axles last year. And went thru the same thing. Ruin a tire ever 100 miles.

I was already to replace the axles when I decided to try and have them staighten. Took it into a tire center that focuses on big trucks  ( stuff bigger than pickups)   They had a large alignment rack that I pulled the trailer in on they aligned all 4 trailer tires. They did it by bending the axles till the tires/wheels came into alignment.  It cost me $80 per axle or $160 for the trailer. And I have had no problems since.

I suspect this is process that just postpones buying new axles. As you start bending and re-bending the axles at some point you will loose the tensile strength and every chuck hole in the road will knock them out of aignment. But for right now, it saved me the cost of replacing both axles and replacing tires every 100 miles.