I'm guessing when the mechanic says the tag axle is bent he means one of the spindles is bent. One of the other members here on Airforums had one of his tag axle spindles break off and the wheel disappeared off into the distance never to be seen again.
The repair shop tried to weld on a replacement spindle with horrible results. He ended up buying a used tag axle and is now back on the road. I would highly recommend you find a new or used replacement tag axle assembly rather than trying to fix the one you have.
That's just my opinion of course.
Air forums # 1674
1974 20' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels, brake drums, windows & holding tanks left to sell)