RTFM (read the manual). You do not need to drill anything to mount a canister.

I have found (tested on the first plane) that it's possible to glue a piece of silicone tubing into the fiberglass belly pan with black RTV. I then added more RTV to make a "bed" for the muffler.

This makes a perfect fit, is very secure, does not rattle or burn anything, costs almost nothing, and the fuselage is completely sealed off from the muffler. Use a tie wrap to hold the muffler in.

I have the silicone tubing in stock, and it comes with the canister/header kit.

TF