Jack the trailer up and take a look at the hubs....might be your about to lose the hub bearings which is making the tires toe out.
Trailer axles dont get bent all that easy.....if you hit something hard enuf to bend the axle you would have remembered that incident. Plus hitting something is not likely going to make both wheels toe out.
Good place to buy a new axle if you need it is a place called Scotts Bargain Barn just west of Excelsior Springs Missouri. They build trailers and might even install.
Scott's Bargain Barn
4025 E State Route 10
Excelsior Springs, MO 64024
Phone: (816) 637-5326
Progressive Marine Insurance SUCKS!. If you hit a submerged object they will try to prove manufacturers defect....stay away from them.