Sorry, didn't read the OP question in full :)
It's a campervan, so the battery will be pretty much "inside". Separated from living quarters by some thin wall. I don't think you have any other choice but AGM. Here is my
UPG $180. Can't tell about long-term performance. LIfespan is measured in cycles, not years. I didn't use it much since bought, so it's still good. Concorde/Lifeline of that size would cost $300.
And, - yes, get at least 100 AH solar. AGM don't like to be incompletely charged every day, same as flooded. I have 500W solar, and very modest energy consumption, so they always charge fully by the evening.