Hi Hoopieguy,

Major congrats! I had a '27 one ton (Lurch) for close to 30 years and I loved every moment! He's living his second life now with his new owners, a non-profit foundation that uses him as an agricultural display at a county fair and is driven in parades. 😉

The gas cap that I had was a 55 barrel cap with a square tower thingee on top for tightening or loosening.  It was made from bronze or brass. I made my own cork gasket out of 1/16 inch thick cork gasket material that went under the lip of the cap and sealed it to the gas tank inlet rim.

I did drill a tiny hole for venting, but to keep 'splashing' to a minimum, I put a short (maybe 3/8" long) 4-40 bolt into the hole with the head facing down towards the inside of the gas tank. I then put a small nut on the end of the bolt as it stuck out the top of the gas cap. I didn't tighten the nut, but left a little room for the bolt to jiggle around in the hole so the hole would not be plugged up and provide a tiny space for air to get into the tank.

To keep the nut from coming off (and keep the little bolt from falling into the tank), I smeared a dab of JB Weld on the nut, which locked the nut onto the bolt. 

So, the vent was there and the head of the tiny bolt served as a deflector for the splashing gas in the tank. A small amount of gas still made its way out the vent hole, but not much.

On my '28 Canopy Express, it has a real gas cap (as sold by the vendors) and it has a vent hole (1/16" diameter or less in diameter) towards the center of the cap. I also made a cork gasket to go under the lip of this gas cap. Yes, gas sloshes around during driving and some comes out of the vent hole.

To keep gas from evaporating out of the vent hole when the truck is parked in my carport, I cut a piece of inner tube rubber to place over the cap, put a 4" or so piece of 1x4 wood over it, and set a steel weight (1x1 square stock, 3 inches or so long) on top of the wood to weigh it down and thus, seal the rubber onto the top of the gas cap. This also prevents the carport from smelling of gas all the time.

Hope this helps, Dean

@rustoholic Thank you so much for the explanations - I kinda thought I would need to do something similar to what you did. I knew I wanted to have some sort of reflector underneath to keep the gas from just shooting up the hole. And I was thinking about making a gasket seal around the cap as well. Thanks again for the great ideas and confirmation.

Regards, Scott (Hoopieguy)

Some of the caps had a leather ring under the cap lip. Most were deteriorated and no longer sealed properly. I made a few seals that worked. I have other caps that seal well enough against the threaded tank opening so no gasket is needed. Yes a tiny amount of gas might seep out on rough roads but not enough to cause any problem. When transporting on a trailer I try to only have ~ 2 gallons in the 10 gallon tank. Never had enough gas spill in closed trailer to make sleeping in the trailer uncomfortable.