I'm assuming some stuff here , I've never worked on a P30 chassis, but here goes. Was the connector to the fuel pump module , a 4 wire connector ? If so there should be wires of 2 different sizes, 2 heavy wires for pump power and ground, 2 smaller for gauge power and ground. Follow the wiring from the top of the tank , back to the main wiring harness on the frame , is there another connector there ? If so disconnect the connector and test for 12v power ( in the first 20 sec. from key on ) from the main harness , and check for resistance to ground , should be zero ohms. I think we can really go out on a limb and figure that if the old pump didn't work and the new pump isn't working , that the problem isn't the pump. So if there is no connector at the frame , I wouldn't drop the tank yet. If you have a relay diagram , that tells what the relays you can see are, see if you have more than one labeled ignition, you had the coach running so if you only have one ignition relay it should be the one that supplied power to run the engine, if you have a second then one of the two could be your problem. When the engine was running did the oil pressure gauge work ? Like I said ECM wants to see oil pressure to keep the fuel pump running. Some times the oil pressure sending unit will have multiple functions , and control the fuel pump independent of the ECM, find the oil pressure sending unit and see if it has 3 wires, 1 wire would control the gauge, the others would be power in and out to the pump.
So you may just have a sensor problem. Also check every fuse you can find with a voltmeter , both sides , a fuse may look good and still not pass power. Guess I should have said that first.
I'll scratch my head and check back later.