We have tried various electric awning heaters in the past.
However, we currently use a Halogen Heater. This has a cut-off safety device button on the base (if the heater is accidentally knocked over the electrical supply is cut off immediately). Ideal for use with kids and dogs around!!!
The element(s), although colourful, do not set fire to anything --- even holding a piece of paper to them they don't ignite!
They are relavitely cheap. I am given to understand they are economical to run, using less than 2p per hour to run when on full power.
We always keep ours in the caravan ready for use on cooler evenings.