We have mixed feelings about a heater for our PUP. On one hand, we only camp between late April and late October in temperate conditions. However, we know it can get awfully chilly on early mornings. If you know of a specific kind of plug-in heater that is head and shoulders above all others, please reply with its name. The same goes for a reserve battery system. As far as we know, the PUP that we bought does NOT have one. Should we add one?