Holiday Rambler routinely installed the generator fuel line higher on the tank then the engine fuel line, about at the 1/4 level. So, make sure you have at least a half tank of fuel and the coach is level. That should rule out this as being the cause of lack of fuel.
Good luck. Holiday Rambler made some of the best make RVs back in the days when they were an independent company. We've owned two HR's and have loved both.
Holiday Rambler Navigator DP, Hummer, and Honda VT1100C Shadow