Those who tell you “want you want” don't know what you want and don't care what you want.
If your “deep cycle” battery doesn't have a published DoD vs. duty cycles data then it's not deep cycle.
If your “deep cycle” battery says “marine” on it then it's not deep cycle.
If your “deep cycle” has a CCA rating on it then it's probably not deep cycle.
Charging by solar alone is $$$ and difficult. Charging by solar
and some other source is inexpensive and easy.
Framed poly panels are a good default choice. Flex panels are expensive and rarely justified.
for cheapest power, 2x 6v flooded > 2x 6v AGM > 12v AGM. Lithium has about the same cost in the long run as flooded lead acid.
AGM benefits from forceful charging.
Lithium suffers from forceful charging
Most vandwellers have lead battery capacity in excess of their ability to charge it. This kills batteries.