No problem.....do you have all the original manuals/documentation for your fridge? If not --- the Internet is your buddy....and the Googles....
I just now scooped up your fridge's documentation and specs from NORCOLD 3163 INSTALLATION INSTRUCTIONS AND USERS OPERATING MANUAL Pdf Download.
12 Volts DC Operation:
15.4 volts max. - 11.5 volts min.;
DC current draw: 11.7 amps @ 12 volts DC - 13.6 amps @ 14 volts DC
Trivia to be aware of with 2 or 3 way Propane fridges (that have the capability to also run on DC 12v power):
Propane 2-way or 3-way fridges use *significantly more DC current to operate* than do DC electric-only fridges. This is due to the fact that the 2- or 3-way Propane fridges are using that DC current to *heat up a heating coil* sufficiently enough to match the BTU output of what a lit propane flame would be doing otherwise in propane mode. (Read: That's a lot of 12v juice to do.)
By comparison, a "12v DC only" *electric-only fridge* uses its 12v current only to power a small efficient compressor....so its current draw is much less.
From the specs, your fridge draws 11.7 amps in 12v DC mode. This compares to my buddy's 2 cubic foot 12v DC electric-only fridge in his Sportsmobile that pulls only about 2 amps.
Benefits of propane fridge:
1) silent, super-efficient when using propane as fuel.
2) long-running on tank of propane! (I can get three weeks of continuous boondocking out of my propane fridge, running off the Sportsmobile's built-in propane tank)
3) 2-way or 3-way Propane Fridge also works nicely when running on 110/120v AC current (on home extension cord land-line)
Drawbacks of Propane Fridge:
1) not the most efficient when running on 12v
2) requires fairly-precisely "leveling" the van for it to work when camped.
3) reported reluctance (in some cases) to operate at high altitude (I've used mine up to/above 6000 feet without any issues however)
4) ****ALWAYS**** requires cutting ventilation ducts through the side of the van to the outside. (To vent the propane gases.) You mentioned what sound like **additional** high-altitude ventilation ducts that you are considering....but remember that **no matter what** you will absolutely HAVE to cut some sort of fairly-significant ducting/venting to the outside of the van for the spent propane gases and heat.
To your query about the ability of this fridge to run on your vehicle's electrical system while cruising: here's where my electrical expertise is reaching its limits....but still, I would think your big Dodge's alternator would have no problem kicking out the juice to flow 11.7amps to that fridge.
***JUST BE SURE...that you're running the correct gauge of wires from your alternator/charge circuit back to your fridge for the DC current to handle. (Follow manual/electrical spec guidelines to choose a wire gauge rated for the amount of amps it will need to flow (as well as total wire length). 11-14 amps of 12v will want fairly decent wire gauge to be both efficient and avoid overheating the wires.) ***
Here's a typical chart to choose wire gauge:
Also, be sure you consider:
There exists the likelihood of your under-hood battery going dead in the rig....if you park it and leave the fridge operating in 12v DC mode for any significant length of time with the engine not running.
Are you building this rig with a second, isolated battery to power the fridge? You don't want to have your main vehicle battery go dead on you (and potentially strand you) if the fridge and other RV items drain it down while you're parked or camping.
Hope this is beginning to get you on track...(and that perhaps some better-overall-versed "RV engineers" can jump in from the forum with more guidance as well.