You won't regret installing the Hobie Bob. Way better than the 1 gallon milk jug I used to use.
Assuming you are using genuine Hobie parts, the rivet cap is designed to 'seal' the hole and make it watertight. The rivets are made out of monel, and any galvanic action can be ignored as immaterial. If its from Hobie, its good.
Make sure your rivet gun is a good one, preferably air powered. Monel is tough, not soft like aluminium, which means it requires considerable power for the 'nail' to be pulled up and properly seat the rivet.
Locate the Hobie Bob shaft in place on the mast, secure it, place the straps where required, drill the holes (using the straps as templates,) slide the rivet cap over the (bottom) end of the rivet, slide the rivet into the hole of the strap and then into the mast, have your helper push down on the strap so that it is very snug to the mast, and fire up your rivet gun.
That's it. Once the mast is down, about 8 minutes work.
To avoid capsizes, try turning out of the wind, (not into the wind, lots of posts on this one,) especially when beating, then releasing the mainsheet. When running downwind, try releasing both the traveler and the mainsheet. Teabagging is preferable to capsizing. Enjoy.
1989 Hobie SX18 Sail # 1947
'Only two things are infinite, the universe, and human stupidity. But I'm not sure about the former.'