Since she's still fairly small, I would start with a 15qt or equivalent (I use Sterilite tubs). Just punch/melt holes around the tub for air circulation, get yourself an Acu-rite digital thermometer with probe & hygrometer, and rheostat or thermostat to control temps - that should do it! Not sure what you're talking about with the bottle caps, but I don't think that will be necessary. Oh, and I'd get the UTH made for at LEAST a 20g tank, since they're not super hot... flexwatt does work better and is cheaper, but shouldn't be needed for just one tub. Good luck & make sure to post pictures of your new baby!

Links to what I'm talking about:
http://www.weatherconnection.com/mfg...29964&mfgno=21
http://www.walmart.com/catalog/produ...44440109016186 (the price is for a set of 10)
http://www.petstuffunlimited.com/zoo...hermostat.aspx
http://www.spyderrobotics.com/products/herpstat.html (more expensive thermostat, which I use for my rack)
http://www.google.com/products/catal...d=0CCoQ8gIwBA# (cheapest option for controlling temps)