I wish to share a simple mounting technique that I have used for mounting my mobile radios inside the vehicle. By not drilling holes inside the vehicle, this preserves the car's re-sale value.
I use the cup holder of the vehicle as the mounting base in tandem with a used plastic bottle.
Use a plastic bottle that will fit snugly into the cup holder of your vehicle. After measuring the plastic bottle, cut it at the appropriate height.
You can install the radio's mobile mounting bracket atop this plastic bottle. Alternatively, you can also mount the radio on the side using another bracket which can be sourced from your nearby DIY shop.
Here is a picture of the plastic bottle and the mobile mounting bracket attached. As you can see, the plastic bottle already has several holes in it because I have used it in previous installations.
Here is the final set up inside a compact car. For this installation, it was not possible to mount the radio atop the cup holder as there was limited space. The radio was mounted on the side of the camel hump and an additional "L" shaped bracket was used.
I hope this article helps in overcoming the challenges you might face in mounting your radio inside the vehicle.
73 and hope to work you
Eddie Valdez, DU1EV