Hi,
what I did, so far, in the flat Dutch polders if I can't charge long enough along the way, is to activate the REx as early as possible (~75% soc) when on the highway, then drive a little on electricity at the destination, if needed. Then, again if needed, some little bit of REx-ing on the way back as soon as possible and where it is the least inconvenient (mostly on stretches where max 100 km/h (60 mph) is allowed to keep the revs down) until I'm positive I'll be reaching home with a few km of battery left.
I'm really interested to know how the little REx is going to behave in hilly terrain.
Regards, Steven