I really only need a few things. A bed, some storage, heating, fridge. I would park in the bowling alley parking lot with the other rv's. mostly 1-2 nights mostly but ocassionally a week
Bed
simple: mat on the floor
complicated: raised bed. plenty of storage space underneath. leave it open for easy access or close it up for a cleaner loor
storage
simple: front passenger seat, milk crates in the back
complicated: raised bed again, or if you need even more than that some kind of shelving unit
heat
simple: sleeping bags and lofty blankets
complicated: propane. There are heaters designed for small boats, and different heaters designed for rv's. both require exhaust, i.e. drilling holes in the van. also recommended: outside propane storage compartment, fire extinguisher, carbon monoxide detector
fridge
simple: don't. the only thing you won't be able to keep is raw meat
complicated: propane fridge if you're already plumbing for heat. electric fridge otherwise, but then also you'll need an extra battery and provisions for charging. I also assume that if you wnat a fridge, you also want a stove to cook with?
think about it and figure out what you need. I personally have the raised bed and a small cabinet/table, but that's it. Started with a propane stove and portable toilet, but ditched them both due to lack of use. draw up a few "floor plans"... vans are so small they don't take long, and there aren't many arrangements that work anyway, but by doing it you'll get a feel for what you might want. How much you want to spend might also be good to think about.
http://forum.mrmoneymustache.com/welcome-to-the-forum/fire-in-a-sprinter-van/here's a thread with lots of people wishing and some people doing. plenty of links to other resources in there if you poke around
