An 18" baby should be in something along the lines of a 12" x 20" tub.. give or take a little. You really can't just go from that to a 6' cage.. you need to have one or two graduating tub sizes. Tubs are cheap, so it's not a big deal.

I like the cages from boaphileplastics.com.. they have the best prices I've been able to find. For heating.. I just use flexwatt.

Leave in the enclosure to feed.