Drilling, if you're not careful, will crack the tub. You can get a solder wand while you're at Walmart or Lowes for about $10.
Start with less holes than more. You can always add more if you need them (judge if you have enough by the humidity reading). You can't un-do holes if you do too many and your humidity is too low. Though a plastic tub isn't too expensive to replace.
Some shows will carry UTH's, some don't. Fingers crossed. And yes, you can use a light dimmer until you can get a good thermostat.