Trust me, you don't want to do it that way. It isn't what body filler is for and I only do this kind of work if I'm forced to. At my last job my manager would ask customers who wanted this done "would you be upset if the rust came back within a month?" 9 times out of 10 the customer would say they would be. Well.. when you tap and fill rust like that, it WILL come back quickly because the problem has only been covered up, not fixed. We almost never do this kind of work even for the people who say they wouldn't care. Shops that do this get a reputation for doing crap work. And rightfully so.
I remember awhile ago I had to paint one of these tap and fill rust jobs. The body technician did the filler work and primed it. There was no rush on the job so the car sat for 4 or 5 days before I got to painting it and by that time there were already small spots where the rust was pushing out the filler. If its doing that in under a week, imagine what it will look like in 6 months.
Do it if you want to, but know what you're getting into and don't expect much from the repair
