Maplins sell ceramic bulb holders that screw directly to the viv but I think the best ones are the arcadia ones as they use a mounting bracket that would allow you to bend it slightly so the bulb holder isn't touching the the viv's top or side depending where you want to put it, on another note I recently had to change the bulb holder in my Beardies viv and although it's plastic It's rated for bulb use up to 200 watts, so you could even use a ceramic bulb in it lol. And as Kelf said if you've got one viv stacked directly on top of another, you could always put spacers between them to allow a bit of air flow between them..
1.0.0 beardie "magic" 1.1.0 100% Het Clown "Cerberus" and "Artemis" 0.1.0 Poss Calico "Ariadne" 1.0.0 Lesser " Kronos"