Shortround6
Major General
Since the F2A-3s were new-build aircraft, there was no issue with retro-fitting self-sealing tanks as you seem to indicate. The RAF Buffalos were also fitted with a form of self-sealing fuel tank so I think your final comment is dubious at best. Irrespective, the lengthened fuselage, extra tankage (whether empty or full), self-sealing fuel tanks, armour plate and additional ammunition all increased the weight of the aircraft.
It wasn't a question of "retro-fitting" the tanks but the way the original tanks were designed. They were not separate tanks but an integral part of the wing structure. The spars formed the front and back walls, ribs formed the ends and apparently the wing skins formed the top and bottom. AS for my last statement being dubious, not all self sealing protection was the same. The British 339E's were supposed to have armor on the front of the the tanks(?) and be covered in Linatex and horsehide leather. The US Navy was fitting rubber fuel cells inside their fuel tanks. Fitting the fuel cells inside the integral tanks may have been more of a problem. The US Navy did fit a CO2 purging system to the Buffalo for the integral tanks as "protection' which did add some weight and increased maintenance. I believe my statement ended with fitting the existing tanks with the type of protection the US wanted to use. The US may not have wanted to use Linatex and horsehide leather