Just finished installing a Norcold MFRT-60 fridge/freezer in one of my 2001 MADP basement compartments.
I did it because our house fridge was needing a new cooling unit & was undependable -- so the Norcold was a "Plan B".
I attached it directly to the house batteries per Norcold's manual + ran AC to it as well.
Newmar suggested that I run the 12V line inside the frame rails, but that was impossible . . . spend an hour on my back inside the basement trying to run wire. No go.
By accident I discovered that I could run 1/2-inch plex under each of the basement doors. The plex fit perfectly and the basement doors did not "bind".
Here are the pics: