Drew_K wrote:
On the snap up brackets, where do you put the backer plates?
You're trying to ensure the the DC brackets are connected well (self tappers in thin steel may not hold well) and you're trying to prevent the face of the frame from being bent. 
For the snap up bracket you're trying to do the same thing, as well as prevent the snap up itself from bending.
My approach is probably the most "overboard" by adding plates to both sides of the frame as well as spacers to prevent excessive squishing of the frame when securing the plates. The DC mount and the snap ups are attached to the plate with studs that are threaded and welded(click photo for more info):

Here's a more normal approach (Click photo for more info):

Another approach would be to put the tube I have on top of the frame through the frame (welded) and then bolt through the frame.
I would also add this: It doesn't take some crazy avoidable event to bend a thin tube A-Frame. It's prudent to do the extra reenforcing from the start.
You can also get riv-nuts from Reese. For a tube frame - I would use these at a minimum - 5 per side. I would set the riv-nuts by building a setting tool from star washers rather than the approach in the Reese instructions.
I think the internal backing plates would add some level of support over the riv-nuts and would be worth the additional work/expense. If you did all the other work a muffler shop could tack the nuts on for you....