I am in the same situation you are in with my 53' panel, cant make a side fill tank work because even with a custom tank I would be lucky to get 12galons of fuel,not good enough. i built a stainless tank that I was going to use as a rear mount on a pickup i was building so it is a bit big at 36"x22"x10", but its about 30galons,I mocked it up and it will work but is going to be really cozy back there,now i need to decide on an inside floor fill or I will move the stock filler to behind the filler as previously suggested,then I will get a long skinny air tank to mount where the stock gas tank was.i dont want anything mounted inside(air tank and compressors)for a clean finish,If you really stare at it and pull a tapemeasure on it a few hundred times it should come together!there are a ton of OEM tanks that are a bit smaller than what mine is that would work nicely for you.check out gastanks.com for some research material and good luck!
