Fuel Filler Neck

I was wondering if anyone has mooved the stock filler neck to the inside of the bed? I am still using the stock tank untill I decide which route Im going with my truck. I need to cut the spout down on the tank but not sure if the fumes will ignite. Sawzaw would me the quickest but I like my truck enough not to watch it burn. Any suggestions??

try and exhaust tubing cutter, rent one from the parts store.

Empty the tank, then fill it with exhaust fumes from another car for 5 minutes.

Just a thought of a problem. Will the metal shavings enter the tank while cutting? Or you planned on stuffing the pipe further down to block any debris from entering.