It really all depends on how you will use your
Boler, and you provided a few clues to that but only clues.
If you dont expect to have shore power available often, then there is no need (or very little need) for 120 VAC wiring or a converter. You can keep it all 12 VDC. You can use a charger such as the CTEKs either mounted in the camper with a way to plug it in to shore power or not mounted at all and brought out when needed to charge the
battery.
I wish I could camp only when the weather was not too hot, but to spend time with family I have to go when its mid-summer so for me A/C is needed so I dont toss and turn all night. If you want A/C then a full 120 VAC side wiring with a breaker panel is appropriate. By the way, do you have or plan on a
fridge?
I would use, or plan on using
solar if I were you. I prefer to have the controller mounted in the camper, and in view if the display is something that will be helpful. I prefer a recording ammeter to track
battery state of charge. Unless you only go where the sun is usually overhead, I prefer to at least start with a portable panel or two. So you can plan on
solar for later addition but I think you will eventually want to use it.
Whatever
battery capacity needed is dependent on load but also on how long you plan to camp between battery charges and you only said not extended. A pair of 35 AH batteries means only 35 AH ideally available and thats not much. If all you have is a few
LED lights its fine, but if you plan on a
furnace, fan, or the like, then likely not. Forget about an inverter with only 35 AHs. A plan to expand battery capacity is also a good idea I think.
A detailed power budget should be drawn up.