Like Steve...

One thing you might consider no matter how you end up deciding to mount it.

What I have done is take a piece of plywood, or better yet Starboard, as large as will fit in the area you are considering mounting the unit to. Measure it and then decide how to mount and make a template of it, complete with the mounting bolt holes. Mount that and then mount your device to it.

So, if you decided to through bolt it in your laz, mount the larger board (the base mount) inside with the smooth rounded heads on the outside and the nuts on the inside. THEN mount the unit on that base board.

The BIG payback comes in a year or so when you (or the next owner) decide to make a change or mount a different or another unit in the same area. It's now simple to take the base board off, or make another one from the template, and make the changes without making more holes in the boat.

I have done this on Guenevere a few times and it pays off every time! I even made ALL of the pickups in the forward clean out plate of our fuel tank. Now, if I want to change the fuel quantity sending unit, it only requires a simple new plate.

Just an idea.....

Greg