Beware of portable gas heaters that are not vented they generate a lot of water vapour as a by product of combustion, therefore not unusual to get condensation problems, not to mention they are potentially dangerous to your health. This Australian link explains the risks:
I admit running cost and heat output wise they initially appear attractive, I bought one myself recently but returned it within 2 days because of condensation and combustions smells.
Electric is dearer to run but much safer and friendlier to your home.