This project was motivated by the fact that I do not like to drill open holes in expensive panels and have something hanging that both looks ugly and always seems to bang my knee when I get into the truck. I decided to put the controller in the cubby under the radio; it may not look factory, but it functions better than having it hanging under the dash (much easier to reach). I can also remove it if I wish. I did mine in my hotel parking lot in about 20 minutes. All I had was a cordless drill and stepped drill bits, so I worked with what I had. If you have the right tools it will come out a little better. I have a Prodigy, which uses a 3020-P harness. There is also a 3021-P, but the truck side is different and will not fit third generation Rams (at least not mine).
*******Follow my advice: do not plug the harness into the truck until you have installed the controller. You will need the wiggle room********
1. Pull off the radio surround trim. It is only attached with spring clips, just be carefull when prying it off the dash.
2. Unsrew the radio (4 screws), then the cubby (2 screws). Unplug the radio harness and antenna, then set radio aside.
3. Remove the rubber liner from the cubby. From the back (RH side) you will need to drill/cut a hole large enough to fit the controller lead into the cubby.
4. Feed the harness up through the back of the dash, routing the wiring so it will have some give. Trust me; it will be tight enough once everything is connected, and zip ties will not be needed.
5. Push the plug through the hole in the cubby and connect it to your controller. This is why you should not connect it to the truck yet; the plug is a bear to get connected inside the cubby.
6. Reattach the radio harness and antenna, screw the cubby and radio back into the dash, and reattach the dash trim. Do not put the controller back into the cubby until the trim is back in place; the brake switch on mine is lower than the trim, which interferes with units operations.
7. Recheck to ensure you are happy with the way it looks in the dash. Finally, connect your harness to the truck's connector and you are done.
I still have room left over for small objects. Prodigie's have a hump at the top of the controller, so it sticks out. There are controllers out there that are flat and will fit much nicer inside the cubby, almost flush. I like the Prodigy and will deal with it sticking out a little.