Not much to say ... as far as drilling goes. It is pretty much straight forward.
What I did, which is visible on the second picture is I made the fuel tank air vent tube ... you can see them both on the last skin of the under side that needs to be drilled.
I have made the air vent tubing based on a suggestion that came from a UK RV6 constructor who said it would be wise to do them rather than doing it later because it is much easier for the access , and there are a few nut plates to installed that would be impossible to install once everything is closed up. I thought it was a really good suggestion and I proceed in doing them.