I'm in the same boat as you, ordered a Lance 855s that will be completed 4/21 for pickup early May. I also have been trying to get as much Battery and Solar work done before I get it so I can have it ready ASAP. Couple of things I have found that changed my path are below and some links that helped me out.
- I ended up going with 3 - 100ah SOK Lithium Batteries
- DC to DC will work great, I decided to go Victron Multiplus 2k Inverter for everything instead since I have an Onan
- One thing to remember, the camper charger needs to have a Lithium capability for the higher amp requirements
- For 200ah Lion's the Solar recomendation will be 400w, mine is 600w and no way I can get that much on the roof
- Check out Will Prowse on YouTube, he covers everything or his website will
- I also liked the information on this site: https://www.explorist.life/
Craig