A safe place to park the minivan is an important element, at least if you're in the US, because so many cities have passed laws against sleeping in cars (yes, including a legally-parked car that you own). Not every city, and every city has different laws. For instance, ironically enough, the suggestion to find a driveway to park in would not work where I live, because in my town, it's a misdemeanor offense to sleep in a vehicle on private property (yes, even with permission of the property owner) for more than 14 days/year. Which is an unusual ordinance, but hardly unique...fun stuff.
OP, you might have already done your homework, so apologies if this is unnecessary. It is definitely worth checking your city's municipal and traffic codes to figure out the legality of sleeping in a car. Do not rely on word of mouth -- I have never, ever found that what "everybody says" is accurate as far as either local laws OR police enforcement practices. If your university has a law school, the easiest thing would just be to go to the law library and ask a librarian for help looking up muni codes. But it's usually pretty easy to do yourself -- your city government's website should have both their muni and traffic codes, and searching for terms like camping, sleeping, and sleeping in a vehicle should get you a list of the relevant laws. If you live near multiple jurisdictions (i.e. have the option to sleep inside city boundaries or out in the county), then definitely check both.
A ticket for sleeping in a car might not be a big deal (in some places, it would basically be a traffic ticket, i.e. dealt with much the same way as a speeding ticket). Or it might be a misdemeanor offense, which can be a somewhat bigger hassle (depending on your current/future plans). Fines are all over the place too. Either way, it's always worth being informed, since it can make a difference in terms of making this work long-term.
ETA: sorry, got distracted before I finished the thought. None of this is meant as dissuasion (I think sleeping in a vehicle makes a ton of sense given the fucked up housing commodities market, and have done it myself). Just that knowing the laws helps you make smarter choices -- from how much stealth is actually required in your vehicle, to where to park, to how often to move. Good luck!