Why no 3 way in Clamshell?

My guess would be venting as mine has two vents below the front window, the vent on the side by the door and finally, one in the floor below the fridge. Don't know where they'd put all those on a clam.

There are advantages to the 12v fridge. It only draws 5 amps when the compressor is running, so it's suitable (and safe) to run while in tow. Second, its very powerful, and the freezer section actually keeps things frozen. It also works in 100+ degree temps, keeping stuff nice and cold. It's also very fast--it cools down in less than 10 mins. Finally, you don't have to worry about the gas and igniting it, along with the problems with thermocouples. Pick your poison I suppose, but if I had a non-CS version, I'd ask for a 12v instead.

Mr_Mrs_Gnome - if you do wind up doing this please post your thoughts. I have thought about this option several times, especially after all the 3-way quirks I have read about.

Pxlated.  I agree with your assessment.  Just observing that the simplicity of the 2-way isn't all bad.    

I still toy with ripping out the fridge and putting in an ARB.  If I decide to do a serious stint in the T@B, I would probably move to an ARB to limit draw on the system.  

Lil - The length of the propane line is probably an issue but the bigger problem is venting. There's in/out burner vents (you'll see them on T@Bs with internal fridges), then there's air intake below the fridge through the floor and finally a powered exhaust vent to exhaust the heat around the cabinet.
Every RV fridge I've seen is set against an outside wall to allow for all this. Would be hard to do in a clam. Almost has to be against the interior wall.

Well, there's a lot of vents you'd need to angle out the side. First, the two vents for the propane burner (air in and exhaust out). Then the two vents that circulate air around the fridge itself (input and the fan powered exhaust). So I suppose you could but you'd have a lot to take into account and re-engineer.

The 2 way is simply installed in the cabinets with no external venting. It has a built in fan for circulating air over the condenser coils beneath, but gets its air from the surroundings.

An ARB is a 12v freezer/cooler - ARB is a brand name...
http://www.amazon.com/ARB-10800472-Fridge-Freezer--Quart/dp/B002Q1INDM/ref=sr_1_2?ie=UTF8&qid=1443057307&sr=8-2&keywords=ARB+freezer

A bit pricy? That's an understatement :-)

Not a clue :-)

After reading the description and some of the answered questions on Amazon, the "draws less than 1 amp" (.87 amps) statement appears to need a little clarification. That power consumption is the average hourly draw to keep an already-cold 50-qt ARB below-freezing in 90-degree temps. The draw while running appears to be somewhere between 3 and 7 amps (couldn't find published specs; those numbers based on comments from owners,) and the "draw while running" number for the 2-way installed in the T@b seems to also fall within that range. I don't doubt that the ARB is more efficient - maybe even much more efficient, but a comparison of ARB's average draw over a 66-hour test period (the source of the .87 number) to the 5-amp draw of the T@b's 12V while running isn't exactly apples-to-apples.