He's going to be driving most of the time.
Most
days*, its unclear to me how much actual
time will be spent driving. I've lived and traveled long term in a van a few times in my life, driving most
days does not always mean a lot of driving
time, in fact sometimes it means the opposite. I average probably 1.5-4hrs per day , with occasional 6+ hr days and many <1.5 hr days, as well as many non-driving days.
Point being OP needs to consider their driving and camping patterns to determine how feasible alternator charging will be for their expected consumption. 350Ah / 50A works out to minimum of 7hrs driving per day, everyday, just to break even assuming consistent 50A charging. I don't know enough about OP's scenario to know how realistic this is or isn't, but for me, it would be
incredibly unrealistic. Over 1000+ days living on the road, I would guestimate maybe 2-3% were 7+ hr days. For someone doing 1-3wk cross country roadtrips, or long weekends with lots of driving, 7+ hrs everyday might be totally normal and doable.
That said, I agree with you that:
Sounds like a job for an alternator-driven charging system.
When stopped for some sleep, and a 120AC socket available, a good high amperage 12-volt DC charger (Aims), and an extension cord (10ga) to the rescue.
For the load the OP is talking about, there isn't real estate on the roof of a standard van for enough panels to charge in a reasonable amount of time.
I think we are of a similar mind here, for a small van sized system with heavy expected consumption, having multiple power sources, and maximizing the power of each source is probably the only realistic path forward (apart from reducing consumption, which is the cheapest and simplest strategy in many cases).