Dennis,
Here is another idea from an old forum posting back in 2012:
https://forum.phoenixusarv.com/index.php?topic=830.msg5975#msg5975The "extension rod" used here is a "Kayalu Toughbar"; they are available in variable lengths--this particular one is 8.5". They work with standard 25mm (1 inch) RAM mounts. I don't know what particular monitor you have in your Sprinter, but if necessary you can typically find adapters for most monitors and GPS units to the RAM mounting system. You may find extra cable slack in your headliner above your monitor that can simply be pulled out (there usually is some extra cable, and they have to stash it somewhere).
I considered using this extension to drop the 7" monitor in my unit. In the standard location it works pretty well for keeping an eye on my toad (camera pointed downward), but my 2552 is totally blind to the back, and I really wanted to monitor surrounding traffic to the rear and in blind spots (especially when traffic gets heavy). With bifocals, and since my old eyes are much like yours, the screen's size and location meant I had to take my eyes off the road, and look upward for several seconds to try to make out what I was seeing. Just too unsafe, especially in busy areas, so I just relied on my side mirrors (which are pretty good on the E450}.
My solution surfaced with Garmin's recent release of their new RV1090 GPS unit. I like Garmin GPS's and had been using the RV770 mounted on my dash immediately to the right of the steering wheel for guidance. I moved the 7-inch screen 770 to my toad, and installed the new 10-inch 1090 in it's place. I've just added their BC 35 Wireless Rear Camera that feeds the 1090, and now have a 10" screen next to my steering wheel for both my GPS and my rear traffic camera. I kept the original overhead unit trained on the toad as a dedicated monitor for that. The BC 35, being wireless, provides resolution a little lower than a wired unit, but installation was simple. The large screen only a foot or so away at eye level means I can keep track of rear traffic without even taking my eyes off the road.
So far, I'm really pleased with the setup, and believe it's the best solution for my situation.
All the best, Mike