Several people viewed my question, but no one posted an answer. I probably reinvented the wheel but here is what I found.
1. The Pioneer ADT-VA133 Installation Kit sleeve and brackets fit my thin dashboard and most Pioneer receivers. I had to slightly enlarge the cutout in the dash. I also made a small adapter so that the back support engaged the existing motorhome bracket.
2. I bought the Pioneer AVH-210EX head unit which is an entry level receiver with one camera input. The unit sounds good and has more features than I need.
3. Next I installed a Voyager CSW3014 Multi Camera Controller so that I could also use the side cameras.
4. The Metra 70-9401 Radio Wiring Harness for Mercedes-Benz matched the connector on the motorhome. Pin locations and wire colors matched the wiring harness that came with the Pioneer radio. For the 3 camera trigger inputs to the Multi Camera Controller, I used the connector cut from the Jensen radio for the wiring harness.
5. Sound from the backup camera uses a RCA output and the Pioneer uses a Mini-jack AV input so an adapter is needed if sound is desired.
6. Finally, hooking the parking brake video lockout looked like too much of a challenge for me to crawl under the dash. I bought a Pioneer Radio Parking Brake Bypass. (I have no plans to watch video while driving.)
As several people have noted, the Store/Use switch must be in the Use position to power the radio. The motorhome is apparently wired so that the memory hold is connected to the chassis battery and the switched input is wired to the coach battery Store/Use switch rather than the ignition switch.
Everything seems to be working well except the backup camera voice. The RCA to Mini adapter has not arrived yet.