I'd say if you use the MH so rarely, you'd definitely be better off with a 5th wheel.

I also didn't know that a diesel engine could suffer of vapour lock...Learned something new today.

If the transient suppressor was not replaced at the same time as the ECM it was asking for trouble. Cummins will not replace the ECM, lift pump or main pump unless the transient suppressor is also replaced, nor will they honor any of those parts warranty.
I can't speak to CAT engines.

Well, i think he was referring to air in the line, on these C12's, there is a bleeder valve that you can unscrew the bleed to air out. Hes a gas guy, doesn't work on diesels.

I never had to mess with that when we replaced those on the Cat engines when i worked at the Bus Depot. MY guess is the diode would be integrated into the ECM

We would like to travel more, but this big pusher is just not family friendly.