Good advice, Mark. I guess I failed to mention this because I've worked with plastic and PVC fittings for so long that I know about their shortcomings.
I do check my RO unit regularly, and I've experienced no problems with it. Since it's under the kitchen sink where I keep the trash bags for the trash can, I see it everyday. Fortunately in this case at least, I live in a high humidity environment, even with A/C. The plastic/nylon fittings tend to hold up a little better when they're not as subject to dry rot.
It's too bad that so much of what's available these days is made from plastic - the ultimate throw away material. But with the price of copper at an all time high, I'm afraid we're stuck with plastic. Of course, you could still rebuild your system, replacing all the plastic with copper...but that might be a little too over the top (even for me with my propensity for doing things like that

).
ETA: The Brita filters don't always cut it with some well water. I have a whole house carbon filter that has at least 20 times the carbon that a Brita filter has. I only use a coconut shell carbon in that, no cheap coal based stuff. As is, the RO unit has two high grade carbon pre-filters that have more carbon in them than a Brita. The first filter in series gets pretty ugly after about six months use - and that's with water that's fairly well treated before getting to the first stage of the RO unit. Having well water that's not the greatest right out of the ground can be a real PITA, but I've learned what work's best with mine. I had no less than three "professional" water treatment companies fail in their attempts to remove the tanin, odor, taste, and particulates from my water. After the third, I'd finally had enough and just figured it out for myself. Where the "professionals" failed, this "amateur" succeded.
BTW Mark, please don't take this as a slam against you as a plumber. It's just my experiences with those out there who, IMHO, give real professionals a bad name. I'm sure that you've encountered them in your work...and have likely had to fix their mistakes after the fact as I've had to.
After all that, tonight our development has a meeting with the county about our getting county utility water run through our neighborhood. It's pretty much a done deal, we just have to go through the moaning and groaning about the initial cost of having it installed. I am
so ready to get on the county water, and relegate my well to irrigation duties only.