Having the same problem with ours, taking it to the Ford HD repair shop tomorrow for the repair. It will be a tank drop and installation of new fuel line from tank to the genset. While the tank down, the tech suggested replacing the in-tank fuel pump with a new one. Nothing wrong with with the present pump, but while tank down, I figured it wouldn't be a bad idea.
I would highly recommend doing the right fix, I thought about doing what you're thinking, but I would be concerned about the safety aspect of installing an extra fuel tank.
Jim & SherrySeward
2000 Residency 3790 v10 w/tags 5 Star tune & Banks system Suzuki XL7 toad