Originally Posted by
karolh
I tend to keep some fuel in my tanks after every flying session as it helps to keep the in-tank tubing flexible, but every now and then I do empty them. The hole in the firewall thing in most cases is to aid in balancing the model by having the engine as far back as possible, but if that is not the case in your situation it's quite the norm to use standoffs. Painting the inside of the fuse ( fuel proofing) is commonplace and is protection against fuel spills like in the case of a broken line or tank.
Karol with my tubing you don't need to keep gas in the tank. The tubing remains flexible .
Regarding firewall holes, yes, I always do that for a couple reasons. With rear carb locations, it's a simple way to maintain consistent air pressure around the carb. Aids carb breathing and mixture control in all plane attitudes. I also install a thin layer of foam on the fuse side of the hole to keep gas spit and dirt or oil out. Velcro keeps it ready for the inevitable accessing that would be needed. I soft mount my engines so the soft mount takes the engine loads. The mount also has no center to match the firewall. The mount only needs enough firewall for the mounting bolts so the center of the firewall is just extra material and is not needed. The two things save 3-4 ounces.
Hope that helps you decide.