We've used a RV-Pro water softener for the last two years. It uses non-iodized table salt (mine uses two pounds of salt) to regenerate. It's worked very well for us.
We have been using a blue On-The-Go softener since 2007. No plumbing problems. I need the softened water for a skin condition. There are other units. But this one fits in the storage available in our motorhome.
2004 Gulf Stream Endura 6340 D/A SOLD 2012 Chevy Captiva Toad SOLD
Wow. I will have to keep an eye on that. DH just brought it home and hooked it up, so I guess we aren't just thinking about it anymore. One thing the instructions warn about is to disconnect it while recharging and nottohook it back into your main system until the salt is cleared.