Under the sink water filtration

Depends on what you want to filter. I have long been a fan of under sink RO systems. I actually install them for people as a side line in my spare time. They work great for residential use, but that's a point not to miss. I had every plan to install an RO in our FW and after much deliberation changed my mind. They aren't very practical for RV use for a few reasons. They require a particular flow rate and PSI that a CG or your onboard water pump may not be able to provide. They produce waste water and the cheaper the unit the greater the amount but this can be as much as 2:1 gallons of RO to waste water. This means all that unused/untreated water end up in your grey tank. And if you are using onboard water you are using that and your pump to feed the RO and subsequently waste that water. They would have to be secured to keep them from moving, they take up a pretty much the whole cabinet so space is a consideration. They can't really be winterized so it would have to be removed to avoid freezing. I could go on and on. I just decided it wasn't practical for an RV. Instead I am looking at Berkey gravity fed RO systems. No plumbing at all. The downside is you have to fill it and wait for the water, but much, much less hassle in an RV.