Not much difference IME. I typically take a one person tent or even a bivy. Since the van is probably carrying the tent the weight and bulk factors are largely negated. Will you be somewhere that it is hard to find space for a larger tent? Do you like more sprawling room? I am generally not worried about bringing gear inside. I typically leave everything that I am not using packed. If using panniers they stay on the bike. In your case cooking stuff and other stuff you don't need can probably stay in the van.