Rich -

Good idea to use multiple model tanks.. No compatibility "issues", and can give a bit more flexibility in locating the tanks... [sm=thumbup.gif][sm=thumbup.gif]

If I read your post correctly, the tanks are stacked one above the other and plumbed so each tank feeds the one below, with the vent on the top tank only....

Refill thru the vent using the field box pump... Shouldn't be an issue, but will require plumbing to do so (Maybe a T in the pump inlet line with a fuel dot at the end that is removed and placed in the gallon jug to refuel the fuel cells in the field box... Nice and clean!

Cheers!

Jim