With leaking wing tanks slowly getting worse I have designed and installed a 18 gal fuselage tank. This is enough volume for my 0235 108hp powered RV3. By being smaller than Vans 24 gallon it doesn’t take up every inch of available space. My tank is round 20 inch diameter 12 inches deep. I added two 1/2 inch OD 1/4 inch ID aluminum thru tubes for anti-rotation support and as a back up support for the two stainless steel straps per vans drawing. It required minor adjustments to brake petals to clear and it would have been better to make tank 19 by 13 or 14. Will try to attack some photos.