I will resist terming this a fuel cell as there is no bladder, just a bunch of foam jammed into what appears to be an ABS container. Unused, have had it for many years. Outside dimensions of ~22x16x7, not counting filler and inlet and vent, should contain around 10 gallons. You could form an aluminum can around it or use it as is?
Labeled Phoenix Fuel Systems. $25 plus shipping, don't want it to go to landfill!