Hi there.
1. Fix the panel/ panels securely with some air underneath to keep them cool. (mine are elevated 75 mm.
2. Thick wires from the panel to the solar controller inside the van.
3. Use wills advice for a good mppt controller - get a larger one as you might want to expand later (you cant have too many solar panels) I have enough so the freezer can still work on a cloudy day (3 amps needed)
4. Get a good battery -go Lifepo4 if you can afford it but see what you can get in your local area cheap.
5. If you have enough solar you might not have to connect your second battery to the starter one.
6. Have a joining wire so you can charge the starter if you need to. If you join them with a really thick wire you can use the house battery to help the starter when it is tired.