Another solution is to drill a 1/8" to 3/16" hole in the cockpit floor instead of the canopy. No worries about fuel residue that way. Here's another trick that works great: Drill a hole where your pilot will be fastened to the floor. All of your planes have pilots don't they? Next, drill a hole in the back of his neck or back. Before fixing him (or her) to the cockpit floor stick one of those little silica desicant (DO NOT EAT) pouches into his (or her) cranial cavity (head). Works great!