hi we tend to put ours on top of an old carpet sample square although I reckon you would have no problem putting it directly on your ground sheet as the only two contact points are the metal stand and the gas canister itself neither of which get hot. Great little heaters use with plenty of ventilation and you will have many cosy nights and no problems.
------------- Andy.... No such thing as bad weather...just the wrong clothes !!!
Stingers right, no heat touches the ground. The Black Cat is angled upwards. Having said that if your tent has a SIG you cant be too careful. In my tent the heater stands on top of the picnic rug thats protecting the SIG. In my campervans' awning, it stands directly on the loose groundsheet.