Ok FM radio is the 3 meter band so you need 0.75 meters of "Ground plane" ideally a circle.. If you can just apply window screen to the undeside of the roof. or to the top and paint over it with snow roof or some like product.
NOTE the radio will very likely work just fine without the ground strap just reception may be.... different.
or extend the strap down so it's a full 3/4 meter long (75 CM) straight DOWN from the whip. it does not actually need to be grounded. (if you mount it so it's over a wall you can easily do that.
For Recieve only nothign is critical.
Now for Transmitters...... Totally different ball game (I have something like 5 transmitters behind me 4 actually work one is not currently in use)
