Switches rated for AC are not very suitable for DC loads; the switching action is slow and the air gap between the contacts is small so you get arcing and burnt contacts. As you say, the current when you are just driving a relay coil is very small but you might want to put a diode across the relay coil to stop the switch sparking when you turn it off.The old Switcheroo.....
At last the rocker switches have arrived (thanks NZ post...). All 5 cost me $12 inc postage so mustn't grumble.
They are rated at 2.5 amps at 250 volts so should adequately transmit enough amperage to power the relays.
The sides of the rad will be sealed to the boot floor, and the bootlid vented so hopefully as the car goes along the airflow over the boot will draw through enough to cool it.sexy bit of radnosity , airflow to the rad?