I heard this somewhere, never done it myself, swear;
Find a golf course just off I-95 & plan your stop for just before full dark. Camp in the woods in the rough of most any course. Keep a low profile & no one will be the wiser. (no bright lights or fire, candle power lamps & camp stove). Catch your winks and leave at dawn before the grounds crew shows up.
I have heard that you can almost always find fresh water from a spigot & sometimes a bathroom will be left open at or near "the turn" between holes 9 & 10 for a quick morning visit.
Finding a relatively secure parking spot is not that difficult, at least I never had a prob.... I mean, that's what I've heard. Golf courses are usually in nice neighborhoods. No worries just park out of the way.
Reminder, be discreet, low profile, one person should be easy.
I haven't done this in years I mean, I've heard this used to work very well for budget travellers although I have never tried it myself.