Should we assume that this bad taste follows you all over the Northwest, and occurs at every campground, numbering in the dozens in at least two states?
If you have repeatedly and recently sanitized the entire system, then that is not the problem.
The temporary workaround until you solve the mystery, is of course to carry bottled water. I know that you prefer not to do that, but you may have no choice, either for the long haul or for a temporary measure. I suggest rather than buy the little bottles, get a large one you can refill/reuse. But that's just me. On long trips, we've also bought water in 2.5 gallon spigoted jugs at the local grocery.
Another possibility is that your existing Camco filter needs replacement. those things do not last forever, you know. If it hasn't been replaced very recently, that would be my first step.
You might also consider that it isn't necessary to filter-to-taste even the water needed to flush the commode, and try one of those Pur brand pitcher filters from Lowes or Home Depot.
Drinking water that tastes bad sucks. Been there, done that. Good luck, and hope you find a solution that works for you.