When I replaced my factory fuel filters/water separators, I installed a shutoff valve on the main input lines to the filters, installed a second input with a shutoff valve and a OMC quick disconnect. Did this for both port and starboard fuel lines. Then I brought two of the 6 gal OMC portable tanks on board one day, hooked them up, closed the main line input valves, opened the new valves, hooked up the OMC hoses, and cruised around a while. Worked A-OK. I did this so that if I ever went offshore, I could have an emergency 6 gal (approx 1.25 hours) of fuel for each motor.
Somewhere in the projects forum is a pic of this setup. When I get some time, I'll go looking for it and link it back into this message.