Ran a vent line from my Tanks INC unit(rollover vent) to where the new gas filler will be ran in side of bed. I used a 9/32 vacuum line. I found this dorman vent cap at local auto parts store. Should do the trick. Used same line and dorman cap on axle vent. This line is kinda small, but it's what came with the Tanks INC pump unit I installed in my tank. So I ran it all the way up so it will be installed in same place the gas filler cap will be, but it will be secured higher than the cap. Once I get the rest of my parts to complete the gas filler setup and get to drive to pump and test it, I won't know if the 9/32 line will be large enough or not. If it's not, I have another 5/8" nipple on the tank I will use instead. But I will have to find a vent cap for that size of line, not sure if they make one that large...
Here you can see vent line from Tanks INC pump unit rollover valve.
.