First thing is that you will be able to communicate in English with them, and this is not such a common thing in Japan. The campervans have heating device that runs on fuel from the main tank – so there is no hassle with additional liquefied gas canisters. You just arrive at the gas station, pour the juice in the tank, set the temperature and the interior of the van gets warm. Of course you need some warm sleeping bag and a pair of slippers, but hey! It’s supposed to be an adventure!
As you will quickly notice, the campervan is not that spacious, so the maximum number of people is 3-4, although make sure these are your good friends. Living in such a small space with random people might of course end with great friendships established, but there is also a possibility that things will go just the other way round.