On an 04' TJ tank there are two vents located on top of the tank (white plastic).
The service manual calls them both check valve's.
On the tank itself, one is stamped CV and the other is stamped ROV. Does this mean check valve and roll over valve?
Next question is what to do with these on a vehicle without any emissions evap. equipment.
The tank is being used as a temp before adding a fuel cell which will be using the stock fuel pump set-up.

yhou have to have them or your tank will collapse from vacumn pressure.

There is an Evap can on '04 TJs. It is located in the passenger rear wheelwell under the plastic liner. Like CJ said, they keep the tank's shape and they feed into the Evap canister as part of your emissions system. Deleting them or moving them may cause MILs.

So it would be OK to let them vent to the atmosphere? This LJ has no emission's on it to run them too.
I know that when the fuel cell goes in that it will have the fuel line running into it and one vent/rollover running out and thats it.
First time using a stocker in place of a cell.

You COULD just vent it to the atmosphere, but without a charcoal canister it will reak of gas. In theory you should only really need one of the vents (I think). You may try a smaller junk yard charcoal canister if space is an issue, like one off a mazda or some shiznit.:D