Piece of cake.

My local hardware store sells "stand alone" motion sensors, you wire them into your existing light. Stick one of those up in the corner of the room opposite the door, and wire it to a 120v coil of a contactor rated for the heaters. If you feed the heaters with 3 wire, then you can snitch the 120 off of one of the heater feeds. ( using the right size wire of course.) materials: motion sensor, contactor, box to hold it all, hand full of wire.
TW
Oh yea, the sensor will have to have its "dusk to dawn" feature disabled, but most have a setting or a "test" feature that will do that.

[This message has been edited by Trainwire (edited 10-29-2002).]