Spare Tire Rack Holes

I removed the spare tire rack on the back of my '99 2D 4WD. Has anybody else done this and if so what did you use to fill the holes in short term? My stereo keeps blowing it out.

When I was going to remove the rack from mine I was was going to thread in the bolts, cut the heads off, and weld up the area. Of course, I was intending to repaint my entire truck at the time so that's why I went for the whole deal.