When I had my MH I put in a wired 7" color backup camera I bought on Ebay and it worked well. I bought a 5th wheel and wanted a camera on it too.
Knowing it would be a pain to wire one from the 5th wheel to the truck I purchased a wireless one. Well, As senile as I am I didn't read it only covers 35' and my 5th is 40' and 60' with the truck hooked up.
I only paid $115 shipped to my door for it so I started to look for one that would go at least 90'. You can find them but they start at around $700
After looking at the unit I cut the wire running to the camera and it had 3 small wires red, black and yellow. I know the yellow is video, the red power and black ground.
I cut the transmitter off leaving about a foot of wire on each end and mounted the camera (license plate style) to the top back of the 5th wheel. Used stainless steel self threading screws. I then went to Lowes and bought 50' of thermostat wire (5 wires inside) and 40' of 1/2 inch CPVC pipe with connectors. I then ran the wire through the pipe connecting it to the camera and up to the front of the 5th wheel. I took off one of the marker lights and wired the transmitter to it and to the thermostat wire using the color coding. I then siliconed the transmitter and pipe to the roof of the 5th wheel sealing both ends and securing it to the roof.
It took about 2 hrs but the camera now works great and I paid only $115 for it. I know a lot of people with 5th wheels want a backup camera but $700 is too much money and running a wire from the back of the 5th wheel to the front, down the front and connecting it to the monitor in the truck is too much work so here is a good fix for it all.
Here is the camera: