First: Unless you plan on driving in the AM, i'd not use the block heater at all.. Use a timer to turn it on say 4 hours before you drive (you will fine tune that over time)
Use of the thermo-cube (I use those on my tank heaters) also good idea, it gets AFTER the timer.
Recommendation.. if there is not a properly wired outlet in the engine compartment already, Use 12 ga wire and bend the wire UNDER A SCREW don't poke it in a hole at both ends. Dedicated 15 amp breaker, and use a 15/20 amp outlet in the engine compartment That's the kind where one slot (neutral) is a "T" shape.
1,000 watts is pushing it for standard RV wiring (14 ga poked in the hole)
Home is where I park it!