I have a 65 that has two frame mounted tanks, with the original behind the seat removed. The caps are cut into the side of the bed, and with the angle of the filler tube it is very difficult to fill them up (which seems to happen a lot with a 460 in it). These tanks are aftermarket and have no vent that I can see. Any ideas?
I thought about some kind of tank where a tool box might be (saw one like that years ago) that could connect to the others.
Any pros and cons or other ideas? Thanks

 

Northern has what they call transfer tanks, I was going to go that way until I found a tank for my '71. Check it out.

 

My '66 had it's stock behind-the-seat tank plus two dealer-option plastic "saddle" tanks under the bed. These two filled inside the rear wheel wells. They're gone and the stock tank is now in the bed and I'm happy. See the set-up in my gallery if you're interested.

 

Check out this article about installing a 65-72 Mustang gas tank under the bed, behind the rear axle: http://www.classictrucksweb.com/tech/0404cl_tank

 

Thanks to all for the information. Little Bro, your solution is great! Nice work.
When I finally finish painting my truck I will have some pics for a gallery. I may end up using the frame tanks that are there already and changing the neck/filler and add a vent to each. I no longer have the original tank from behind the seat to be able to move it to the bed.