I just went through this on my new 4150 this weekend, and traced everything by using the HD antennae and a spare 50ft coax cable as a signal check. It's quite likely they are the same layout.
In that cabinet with the water hookups and four coax outlets, here is what I found:
Step A:
Far left connector (when looking in the compartment): CATV connection for cable TV at an RV park hook up. The coax cable behind the panel is colored orange.
2nd from left connector: Grey colored coax cable - I am using this one to feed satellite signal from a ground mounted (not roof installed) Direct TV dish to feed the signal into the camper.
3rd from left: Black coax cable that does not seem to connect to anything inside the camper, I believe it likely goes to the roof as a feed for a roof mounted dish or dome - presumably the other end would be under the HD antennae plate? If that is the case, and it were to be used and hooked up as intended, I expect a jumper coax would be used from this outlet in the water compartment box to either the 2nd from left connector (grey coax) or possibly to the 4th from left connector (black coax below). But that is an assumption at this point.
4th from left: Black coax cable and the label says "feed to TV one". Thanks to the wonderful Heartland labeling, I have no idea which is "TV one" but it doesn't seem to be connected to any coax ports in the camper. Perhaps it is supposed to be. Perhaps it is for an outside television. However I am reasonably sure it is a dead line unless a roof mount dish is installed. I didn't bother to chase it much as I had already found what I needed for my intended purposes (ground mounted dish).
Step B:
In the belly storage compartment on the other side of the camper (side door side) there are two coax outlets. Removing the cover shows one black coax cable and one grey coax cable (remove the cover to see which is which). The black cable port is on the same circuit at the HD over the air antennae on the roof. The grey coax cable is on the same circuit as all other grey coax cables in the camper (2nd from left connector stated above in the water compartment box).
Step C:
My 4150 has an outside TV under a door in the side of the camper up by the pin hitch. If yours does too, or is wired for one, removing the coax cover and following the same process as in Step B will result in you defining which coax outlet is on the grey cable circuit (I am using for satellite) and which coax outlet is on the black cable circuit for the HD over the air antennae.
Step D:
Removing the coax covers in the main living area by the couch will also show which coax outlets are on the black cable circuit for the roof mounted over the air HD antennae, and which coax outlets are on the grey coax cable circuit. In my unit, I have one black cable circuit for over the air antennae and two grey cable circuits in that area.
I didn't bother to remove the remaining coax covers in the main bedroom or toy hauler area, as by this time I had defined that one coax outlet will be on a black cable and the second will be on a grey cable in those areas. So for me, one for over the air HD antennae and the other for the Direct TV dish. So if I am getting the wrong signal source I will simply swap the cable to the other coax in those areas and label them at that time.
I used a label maker and labelled each coax outlet as "SAT" or "ANT" respectively so I never have to pull those covers off again.
Hope this helps anyone else going through the same fun and games.
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One last thing... I have AT&T U-verse at the house but had one Direct TV receiver still operating for my outside hobby shop / camper storage shop.
I called Direct TV and told the retention dept that I was going to shut off my Direct TV account and go to Dish so I could use the pay as you go plan Dish has for my camper.
Direct TV has the same plan, they just don't advertise it. So they knocked $45 / month off my bill (due to limited camper use) and allowed me to use their pay as you go plan. Sounds like it isn't common knowledge that Direct TV offers a similar pay as you go plan, although it is by calendar month. I'm not sure if Dish is by month or calculated by the day(s) turned on.