This cap is not my favorite but it should solve my venting problem. I constructed a spanner took to carry in my tank bag to help me loosen the cap with gloved hands in cold weather.
UPDATE: The 4th time I opened this cap its o-ring came off. My vent mod worker perfectly but I have deemed the cap itself unreliable. Next.
I found these EZ-GO golf cart rollover valves at Gilbert Outdoors for under $10 each. I ordered them by phone and saved $7 off the minimum shipping rate on their website checkout. 863-763-6434
UPDATE: These valves gave a bit too much resistance to stop the transfer. I'm sure they'd work fine with a fuel pump system.
The tank straps are 36" hose clamps covered in 3/8" shrink tubing.