Here’s a tip I use. I buy those extra-long ¼’’ drill bits and use them to drill your 1st hole through. With the long length, you can use the shank as a guide to help ensure you go straight where you need to. Then what I do is use a holesaw, but I turn the bit it uses as a guide upside-down, so it doesn’t try to cut and walk off the hole, but rather just serves as a pilot.
You really should cut this hole over-sized, then wet out the exposed wood core with a thin 2-part epoxy, like either the smallest bottle of Git-Rot you can buy or West Marine sells a 2-part kit of thin epoxy, though they sure don’t give it away!
Just as that thin epoxy kicks, I’d add thickened epoxy to the sides of the hole to build up the edge of the hole with at least a 1/16’’ border of epoxy. Put it on ‘too thick’ here too, as you can then use the real bit/holesaw size needed to cut your hole through the epoxy.
Doing this will leave a permanent ‘ring’ of epoxy between your outriggah mount and core, making the installation waterproof.
