Hi Mike,
Though you may not have a traditional UDC, you should still have access to the backside of the city water inlet. Likely from the area behind an access wall, back where your furnace, water pump and water heater may all be - though I admit I am unfamiliar with the utility configuration of your brand and layout.
So, if you do have access to the backside of the city water inlet, it likely has 1/2" male NPT threads with a piece of vinyl hose or PEX hose connected to it. If it were me, I'd want to grab the water there and run through my filtration system, then return the output of my system back to the line that was connected to the inlet and feeds the coach.
I'm doubtful there is any GHT (garden hose thread) connections in the coach - just on the outside for city water in and perhaps black tank flush. Most all you'll be dealing with is 1/2" NPT in male and female.
In my current coach, I created a wooden frame to mount my filtration (and RO) system on, then I screwed that frame to the floor. Once in place, I plumbed it in as I described above.
Here's a link to that system.
I tried to use as much all-plastic connectors as I could, but I found them to be not as well constructed as the mostly-brass Sharkbite (and similar) brand connectors. Going forward, I will be favoring less all-plastic connectors.
Over the years, in 7 coaches, I have used various filter types and configurations. I feel that purchasing a multi-stage filtration system from
RV Water Filter Store or similar is a great route to go. Rick (or his fulfillment people) will configure the system to your specifications, right down to the connector types and sizes you want. The filter cartridge pricing is decent too. But there are other online sources for all of this stuff.
Wishing you the best!