Speaking of fuel proofing and leaking fuel tanks..........here's my story. About 10-12 years ago I had my Sig Rascal 40 ARF at the flying field and started to fuel it up for it's first flight of the day. Had the fill line hooked up to my electric fuel pump, had the vent line attached to a catch bottle so I can see when it's full and not make a mess, standard fueling procedure for me. So I hit the fuel pump on button and stand up to have a coke and chat while it's fueling itself. It was sure taking a long time to fill up and when I looked down at the Rascal I could check the fuel level by looking at the transparent red covering in the rear fuselage area! Yea, it was about half full. The fuselage was about half full! A nice fuel level line was clearly visible thru the semi clear covering. Oh s#*% ! There was a quart or two of fuel sloshing around inside the the fuselage. I quickly removed the wing and poured the "extra " couple of quarts of fuel out thru the wing opening. What a mess. The servos, the RX, the battery foam, and of course all the interior wood were soaked with fuel. In short order I was on my way home where I stripped all the bits and pieces out of the fuselage (RX, servos, wiring, pilot, and of course the bad fuel tank). I then filled, and I mean filled, the fuselage with kitty liter type oil soak particles. A trick I learned in my race car building days was to crush the oil soak grains into a powder for maximum absorption potential. I let the powered oil soak do it job for about 3 weeks, I stirred it around a few times in there, added new powered oil soak and was able to save the airframe. The firewall was sealed with epoxy but the inside tank area had not been done. The long term result is that the plane stills flys today with all of it's original covering intact. All of the original electrics, RX and servos, were immediately opened, cleaned with alcohol, allowed to dry and were reused in the Rascal. No amount of inside fuel proofing could have saved me that day but quick action and having a plan of attack solved the problem. I'am sure that I didn't get 100% of the fuel out of the wood but I got enough that the Rascal is still serviceable and flying. Bottom line is that inside fuel leaks will happen, so fuel proof as much as you can and have a plan to clean up the mess when it happens, because it will happen.