Join Date: Aug 2012
Location: Ann Arbor, MI USA
I would recommend a temperature controller (recommend Inkbird or Vivosun) coupled with a seedling heat mat (check Vivosun). I used a similar setup to heat an insulated fermentation chamber for brewing. It worked well. If you go with both of the Vivosun products you could probably accomplish this for less than 40 bucks if purchased on amazon.
You would have to drill a hole, but I think long term that is going to be your best solution.