Go here for information on portable water softeners.
On The Go Water Softener It's the website for On the Go, but has good information and most, if not all of it applies to the Flo-Pur softener as well. Camping world has them both on sale right now. They are both 8000 grain units, so they have the same capacity. The On The Go double model is attractive if you winter in Arizona due to really hard water there.
You can use potassium chloride instead of table salt if you're watching your salt intake. But, for the portable units you have to crush the pellets into something resembling table salt yourself to make it work.