Also I disagree. All you have to do is block the vent hole that's in the cap, because the fuel escapes there in my opinion. I modified my fuel filler cap years ago with a seal that blocks the vent hole (not needed, tanks are vented fair enough thru the tubes). Had no fuel spilling ever since. The seal is like this:
https://www.ebay.co.uk/itm/282486506233Also note the extra o-ring I made up and placed in the filler neck.