I bought a wireless backup camera from Costco (Digital Wireless Backup Camera with 4.3" LCD Screen by Rear View Safety). My wants were slightly different than yours, but maybe my experience can help with your wireless questions...
I wanted the screen to be in the backup mirror like my daily driver at the time. I thought that was a nice implementation without an extra screen to place and/or advertise electronics in the vehicle. So, that was one primary basis for my choice of system.
I wanted wireless so I didn't have to hassle with wiring, as our coach was not pre-wired. I figured since the coach is fairly short (25'9"), the wireless signal may work. Costco has a good return policy, so I tested the unit at my coach's length before installing to see if it looked okay. Glad I did this as the first camera was a dud. Had to order a second version. It worked.
In addition to not wanting to run wiring, I didn't want to drill holes in the back/exterior of the coach. So, I mounted the camera using VHB tape to the inside of the rear window frame pointing out the window. This window is just below cabinetry within which I had access to the wiring for the rear clearance/running lights. I wired the camera up into the cabinet and tapped into power from the running lights - now I can choose when the camera is during the day by turning on the running lights. Obviously, this means it is always on at night when the headlights are on.
The camera has worked great! I'm pleased with the performance, especially for the price ($170) and the relatively low-hassle installation. I didn't test longer lengths to see what sort of range the wireless has, but we've been pleased so far (we installed last summer).