I just spent 6 months in my minivan. I suppose that is about as much space for one person as B would be for two.
I had NO trouble finding space for lots of clothes, food, water, books, tools, etc. Weight was the limit, not space. I had way more stuff than I needed -- two or three weeks worth of clothes and food.
I did not hang out in my van during the day. I hung out outside -- sightseeing, or in a lawn chair at camp. I put up an awning on rainy days. I did go to bed early, and lie in bed surfing the net or reading or watching tv.
I stayed at motels a couple of times. I think this is probably much easier in a van than in a MH. The rest of the time I camped. I liked having both options.
I used my bicycle as a toad :). You might consider ones with electric assist, or a moped...
I used campground showers, bathrooms, and laundry almost exclusively, although I had backup systems in the van for when I needed them.
Yosemite has free, hybrid buses. I think Zion does, too. The parks try to discourage people from driving around in private vehicles.