Mike, first, if you are hooked to city water, and turn on the water pump, the system will default to the source that has the best pressure. Many people hook up to city water, use it to top of their fresh water tank, and the hose attached to the water spigot, but shut-off. This ensures that the water pump will always have the best pressure.
I have been using an On The Go portable water softener for about 7 years. It actually produces better soft water than our sticks and bricks unit. We have a stacked washer and dryer, and Becky uses it often. Using those appliances causes me to have to re-generate about once every week or week and a half. It takes about an hour to do, and uses 2 of those little Morton salt containers. There are two models, a standard, and double standard. I use the double standard. I think I paid $183 including shipping from RV Upgrades.