Definitely talking about petrol engines by the sound of it. As for your question, why not just buy a generator? Got everything in there- alternator, built in fuel tank, handle/chassis and power connectors. Not quite portable, but carrying round a 23cc and fuel tank is not quite portable (or safe)

Reliability should be in 1000's of hours, as long as using correct mix and not overheating. Generators are static and they last ages, but model engines are designed with moving air as well as the cooling fan (next to pull start) in mind. Compare temp. of RC petrol plane engine temp with the propwash to the same engine, but in static car.

A "motor" is a not a petrol engine btw..a motor is electric.