SHRED - seems you have a few threads going on the same topic.
First question - what do you want to filter? Chlorine, Chloramine, dissolved solids, fluoride, Gen X (Teflon), Bacteria etc.
An RO cares for all that, but as I mentioned in my other post they are not really practical for RV use. That was my plan, but water usage, waste water, PSI requirements, space and winterization lead me the conclusion that residential RO systems are not practical for RV's.
Usually 2 stage filters are the best approach. First stage is a particulate filter for water entering the RV. This can be in line in the hose. This really protects your plumbing more than anything. It's a sacrificial filter and easy and cheap to replace the cartridges. You can use an in line or whole house particulate and carbon block dual set up, better but not perfect.
Single in-line filters at the sink are usually carbon/charcoal and remove the smell and taste of chlorine. I haven't seen any claim that they actually remove the molecules completely, but enough to mitigate smell and taste. They won't remove Chloramine which is widely used as an alternative to Chlorine in many municipal systems. To remove chloramine you need catalytic carbon - very expensive unless you are using RO.
Finally, if you want pure drinking water that removes every contaminant and left with plain H20, you need RO. But again, under sink RO systems are not practical for RV use. To me, the Berkey was the perfect compromise. RO water without all the plumbing. The downside is filling it, moving it etc. But for an RV, it's a decent solution to good water.
The obvious difference in what you want to filter in your house vs an RV, is that the water supply for an RV changes every time you go somewhere different. Not all public systems are treated the same and contaminants and water quality will be different at every location. That's the primary reason for an RO alternative. It will remove everything, every time. Single, in line filters don't. But again, some people don't care. That's why I asked - what do you want to filter? How clean do you want your drinking and cooking water to be? There's an option for every level of filtration, from basic particulates to all contaminants, and everything in between.