I could give you a long story about installing a Shurflo 4.0 pump but I'll cut to the quick. Don't do it if you are trying to do much more than deliver water to a single faucet! Just save your money and stay with the stock pump. If you want more and preferrably better pressure at the shower head and don't want it to fall off when someone else is getting a drink in the kitchen you are in for a frustrating ride. Shurflo will be great to try and help you solve any problem. They will stay on the phone with you, send you new pumps and maybe even let you talk to an engineer. But, in the end, you will only be lucky if it works. I have a 2003 35ft Itasca Suncruiser with a simple plumbing system. All I wanted to accomplish besides delivering water to the outlets was get more pressure at the shower head. I got one pump to work for about a year but after it died I never could get another one to work. I can get it to pump water to one outlet but as soon as you turn on a second the pressure drops off and may or may not build up again. I have adjusted the center screw but that does't solve the problem.
For those considering an accumulator, Shurflo suggested I install one and then kill the software at the pump. They never told be how to disable the software (I'm sure they would have helped me) but I wasn't interested in that solution since I felt I had paid good money for a pump that is supposed to be intelligent enough to respond to increased demand. It's the way they promote it. I don't understand why delivery of fresh water is such a complex problem?!? Listen to the writer who has now installed a second pump with a sophistcated backup wiring system so once his first pump fails he can switch to the second and then I suppose make a beeline to the parts store to replace the first before the backup fails. My backup is just a simple second pump. It now takes me about 10 minutes to replace one and I'm up and running but still...All this on a 100k-200k-300k investment. I have been MHing for 7-8 years. I know we are riding in a fairly complex house on wheels and sometimes on some very rough roads. But, we can't figure out how to build a pump on shock absobers that will consistently deliver quality service to maybe a couple of outlets concurrently...and by the way...leave it on all the time or maybe shut itself off after X minutes if it is so important to turn it off if you aren't using it. I don't believe it.