Join Date: Sep 2007
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You can temporarily seal those hardware holes with tape -- I've come to prefer aluminum ducting tape (not the fabric "duct tape" stuff) since it's very easy to cut to just the right size and shape, withstands weather well, and comes off cleanly. Gorilla Tape also works well, but tends to leave a little adhesive residue behind which can usually be tacked off with the adhesive side of a fresh piece of tape. Adhesive remover will clean up any stuborn hangers on.
As far as permanently sealing those hardware holes, I think your first decision should be "how inconspicuous do I want the repair to be."
If your coach roof has a paint finish, I'd fill them with Cabosil thickened epoxy, fair, prime, and paint. If your coach roof surface is unpainted gelcoat, then I'd fill them with a polyester filler, fair and then finish with gelcoat. The epoxy will be a stronger bond, but since this is a cosmetic repair it's not critical. With either option, make sure that you clean out the openings well (a Dremel comes in vary handy for this step), and wipe with acetone before you apply your filler of choice.