My quest to enrichen Jeff Bezos continues.
Our '98 DSDP came with  Duo-Therm 13.5k A/C units with heat strips and a 4-button thermostat. This being Texas, the A/C units were struggling to keep up in the heat. They were also noisy and came on with a big bang/thud that was disturbing when you're trying to sleep.
I spent some time researching my options, spent some quality time on the phone with Newmar and Dometic, then started buying. I got a CCC 2 thermostat in white (Dometic part 3314082.011),  Dometic Blizzard NXT 15k heat pumps (Dometic part H551816), and the replacement plenum (Newmar part 123981) and cross braces (Newmar part 04460Z) from Newmar.
Removing the old units was straightforward. Pull up the silicone covering the lag screws and unscrew them, then disconnect the wiring (did I mention I turned off the electric first?).
I have read a lot about Newmar's snowflake plenum setups, but I don't know if I'd ever actually seen the comparison between their weirdo original setup and the new replacement plenum that's like the entire rest of the world uses.
See that straight part bisecting the new plenum? The gasket on the new A/C separating the intake vs. output plenums (plenii?) goes across there, and there needs to be some support there. Newmar makes some rather expensive ($48/ea.) aluminum support braces for this. I'm not sure what those braces go to, but I can tell you with authority what they do NOT go to - a '98 DSDP. I ended up fabricating some braces myself.
Braces now in place, it was time to mount the replacement plenum base, do a little wire management, and use 3M foil tape to seal up the ductwork.
I must take a moment to profusely thank bruceisla for sharing with me an install manual for the Blizzard NXT
(which mine did not come with). Without this manual I'd have never figured out the dip switches. Speaking of which, my unit differed from what was depicted in the manual, as my control box was sealed up in the plenum and not on the side. I'm presuming it was because I ordered the heat pump variety (Dometic part H551816 AXX1C0) It was buried pretty good:
I got the back one set for Zone 2 and buttoned everything up.
Moving to the inside, I installed the new programmable thermostat and followed the instructions to set it - turn it off, hold down "Zone" and "Mode" buttons simultaneously, then after it says "INIT" plus any detected zones, hold down the power button for a moment to exit this setup area. It was now ready to go.
These units are, to my ear, a little louder outside the coach and a little quieter inside. Notably, they come on very smoothly without the WHUMP that the older Duo-Therms exhibited. They put out a whole lot more air through the vents than the Duo-Therms. All in all - a very worthwhile expenditure of a day of my life.