Solar panel and alternator delete
 

I aim running without alternator.

I have the starting batterie kept in place for starting the car and the cars alarm.

In the trunk i have deepcycle amg batteries for powering the car.

I want to mount a solar panel to the dashboard to keep the starting batterie topped up. So i only need to hook the charger to the trunk batteries.

What solar panel should i use?

Use the biggest solar panel that fits!

I tested panel inside the vehicle. Panels inside the vehicle are almost useless. Take what every the rating is on the panel and reduce it by about 60%.
Solar panels are only going to work placed on the out side of the vehicle.
It takes at least 50 or 60 watts, bare minimum to keep the battery up in my suburban and that was just driving it 8 miles a day.
Driving 50 miles round trip took more like 100 watts to keep the battery charged.

I should try my solar panel outside the car. I have one 6" x 12" panel on the passenger's side visor, right up against the windshield.

To go alternator less in Belgium you're probably going to want the whole roof covered in panels.

I'd run a quick connect out of the hood so that the car can be plugged into a charger with minimal hassle. Both the starting battery and running battery are in parallel, right? If so, both will charge at the same time.

I have a small 5 watt solar panel installed on my truck, but that's only because it can sit months at a time.

No. The starting batterie is only hooked up to the starter and the car alarm. The deepcycle batteries are a separate circuit for all the cars accesories.