Thanks guys, in hindsight it does seem like a bit of a bad idea.
I think I may have been getting a bit carried away with the rivet gun lately. Note to oneself: Not all problems in life can be fixed with rivets
I've just been digging around the tool cupboards at work and found a rivnut set, so I might just borrow that one evening.
Will IVA man be happy if I use a riv nut to attach the tank's earth strap too?