Thanks everyone!
After what you have said, I'd only add the second one if it had a seperate pickup and by passed the other pump. I'd have a second waiting instead of being on the side of the road or in someones shop.

 

Another alternative (although some would argue not as good!) would be to go down to the closest Cummins dealer and buy a spare engine mounted lift pump ( I assume that by yours being an 04 and your concern you haven't had the intank conversion done yet). This way if yours starnds you it can easily be changed on the side of the road compared to trying to deal with an in tank unit if it fails on you during a trip. I do know that Cummins still sells the engine mounted units.

 

I don't know about being better able to explain relays... I'm ok as far as electronics are concerned... more of a bending pipe/pulling wire tradesmen. Some electricians I know, unfortunately, wouldn't know much about relays and pumps if they were smacked in the head with em'...