You have gotten lots of good advice so far, I have seen this a few times and fixed it with a free diagnosis tool.
Temporarily bi pass all the safeties for power to the fuel pump (ignition switch, oil pressure switch, inertia switch) with a jumper wire from the chassis battery, all the way back to the fuel pump (please put an in-line fuse in this jumper). You should hear the fuel pump running when you do this.
If the RV starts and runs and does not die again you know you have an intermittent voltage supply problem to the pump.
Just one more thing to try, best of luck. These kind of issues can drive you nuts :E