Vent? We don' need no stinkin' vent...
Seriously... although I didn't hook up a vent when I installed my set-up, I am going to now, after reading these posts. I do use a non-locking vented cap, but the more I think about it, the more I want some sort of filtering material between the inner tank and the outer air.
I mounted my tank as far to the passenger side of the bed as possible, and this allowed a space of about 10" X 8" on the driver's side, beside the tank, for storage of Stanadyne lubricity formula and drilling holes to mount the pump etc. I drilled a 1 1/8 inch hole through the bed and used a grommet to protect the fuel line.
I mounted my solonoid selector switch and the pump to the underside of the bed, drilling 1/4" holes through the bed for the bolts and then covering the tops of the bolt heads with undercoating to mimic the sprayed-in bedliner. I mounted the NAPA filter/separator to the inner fender between the frame and the outer fender. Then I drilled a hole into the filler tube, stuck a piece of brake line into the hole and when I was getting my ATS trans re-build I asked the guy welding the TC to weld my filler tube too. They were happy to do so, (after I removed it) and then I just connected the system up.
One of the reasons I went with the Aero tank is that if I ever get busted and forced to change it, I can change it to a full Aux. tank. The other reason I went with Aero is that I could drive there and get it without paying truck freight charges.