Ok, first I do not think the radio itself makes all that much difference.. Though it can.
What matters is the antenna.. proper length is 18 or 36" (there are some other possible lengths as well) as the wave length (300/162) is just under 2 meters or right around 2 yards.
The BEST, antennsa however are external.. So if your radio has the ability to use an external antenna, Put one ON THE ROOF, of the RV (or on the ladder or on the arm of your Winegard) use a design that either includes it's own ground plane (Radial elements that stick out) or needs no ground plane
(You can find several antennas on the following Link, these are designed for a nearby ham band (144-148 MHZ) but will usually work with Weather band (162) though shortening them to the limit of their stop may help. (do not cut, use adjustment)
MFJ Enterprises 2 meter antennasThese antennas use 52 OHM coax NOT RG-59/RG-6 but RG-58 or several other numbers.
If you have a unit with a FIXED antenna. like I do, you can bring the coax in then fix a connector as follows... Solder a wire to the center pin, wrap twice around the "finger" style antenna, and solder the other end to the body/shield.
It works by inductive coupling.