If you look up cellphone booster . On Amazon
You will see a variety
Like said above, antenna separation applies to all of them
The stronger the transmit signal the more separation needed
It is pure RF physics
Also proper mounting procedure
If you take a vertical mount antenna and put it on an angle or lay it down
You will get more feedback to the inside unit
That's part of the physics
Signal orientation
Two failures
Are you using the direct 12v connection?
To the truck or to the camper
What is the voltage on the connection ?
I would suspect high D.C. Voltage might be a problem
