It has happened to me also
The first time I had to take my unit to a truck mechanic to look at the gas intake line. He said it was drooping and he fixed that. Was working fine for about a year then on my last trip it started again. The vapor canister was not responding so they replaced that. He also told me to place a board under my back tire at the gas station and change the angle a bit. He said he has had others have this happen and this seems to help. When I was getting to a gas station and unscrewed my gas cap I would get a large expelling of gas fumes and gas would spray out. I knew it was not venting so I would undo the gas cap every few hours to release pressure which seemed to work. Try pulling onto a piece of wood about 2 inches tall at the pump and change the angle. It is awful to put gas in I know but it will go just do it slowly and never overfill.
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