Yes, heat (above about 85) does cause protank flooding. My solution is one of those travel mugs that have the liquid in them and are meant to be frozen - freeze the mug, use that as a PV holder in your car and, if you are going out for all day, a small cooler with those reusable ice packs wrapped in a towel (to soak up any condensation) is a must have - cool juice, cool spare tank, cool rig.
Yes, I know these things act more like pets than PVs at times, I swear it has a mind of its own. LOL
Higher VG (like above 50% helps too but, that kills the TH unless you are doing a spicy/hot flavor or lots of nic to compensate for it.