if you get the kenwood units, you only need to drill 3 holes, one for wiring and 2 for the mounting rods that go thru the hull, that's if you want to surface mount it. flush would require much more cutting than i would be prepared to do, and it's permanent. if you switch to a different brand in the future, might not fit and now you're stuck with a huge hole..

where to mount it is all personal preference.
here's a not so great shot of the one on the back of mine...