I too have been down this route, I ended up buying a 100w flex panel off eBay, one similar to this.
https://www.ebay.com.au/itm/100W-Fle...QAAOSwQS1Z6aJy
Basically I have an Mppt regulator in the back of the truck, next to my drawers and an Anderson plug. the panel fits nearly between back seats and drawers and I throw it on the roof or the ground when I get to camp. I like the idea of the flexible panel, takes 2 seconds to setup and I use my rack a lot so did not want one permanently. It was a lot easier than the under rack idea and I have a 10m extension cord so can park in the shade and run the panel in the sun
You can see below the cable running from the back left of the drawers onto the roof, panels so thin you can't even see it. The panel works well I had it in a previous car and it ran a 65L fridge at Fraser for a week without starting the car on a 100ah battery. I have a 90AH AGM under the seat in the jeep and it runs a 40L engel no dramas.
Here it is on my old car, I just use a couple of sand pegs and tilt it up on the beach, works a treat.