I use Marine Tex epoxy for this. Works perfectly. Little trick I do is put a piece of masking tape over the hole, punch the tape out covering the hole and pick the "hanging chad" out so you have a nice border around the hole. This way can mash that epoxy into the hole without making a sticky mess everywhere because it won't come off.
I then drill a small pilot hole when its hardened. It hardens very quick but I let it set over night. Then I put a dab of white caulk/seal and replace the snap.
Or you, can attach your carpet to ply wood and not need snaps on the boat!

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Former owner of:
1996 Four Winns Horizon 200 5.8L VP
2006 Four Winns Horizon 260 8.1L VP
2007 Sea Ray 290 Sundancer
Current boat
2004 Sea Ray 290 Sun Sport Twin 350 Mags
