I would be more concerned about developing fatigue cracks on your frame. You seem to have created a cantilever condition that will probably cause some deflection of the frame at the mounting area. You might have considered welding a flange to the end of the tube that is about the same height as the frame rail. You could then attach each tube with four or six bolts over an area of about 6x9 in. Besides being stiffer, there's no risk of damage to any high strength steel from the heat of welding.
Dan
A good mechanic can fix their own mistakes.
I blow my horn before it happens, not after.
When your in a hurry...slow down.
Ignorant is blist.