i'm from phx originally and am here now. and am van living. arizona in general is pretty negative towards homeless people, or travelers, i have never experienced any other place like this. people are right that tucson has always seemed better, i used to go down there alot to see punk shows. if you were gonna come here you are about to miss the good window,
there is no way in hell you wanna be rubber tramping in phx, or tucson once winter is over. prescott area, or northern az is good for summer. just to give you an idea, there are plenty of days it never drops below 100 degrees even late at night. all the concrete soaks up the heat during the day and releases it at night. its called a heat island. out in the desert it may cool down a bit at night, especially near a body of water, but still i would avoid this area. but you could drop in and decide it sucks and head north.
alot of homeless people seem to sleep at night in a wilderness area called the rio salado park just south of downtown, probably the best area to sleep any time it is hot. also small tent city near homeless services around 10ave & jefferson just west of downtown (not far from my old neighborhood). i've walked through this area plenty of times, but i don't think i would sleep there. it is generally a pretty rough (potentially dangerous) area.
if you make it out before i bail i could show you around a bit.