if the temp in the greenhouse is 30° that's part of your problem, xmas lights aren't going to help. you need to put a heater in there to warm the whole place.
use a milkhouse heater(23prong) with a thermostat.
Milkhouse:
https://amzn.to/2Tesish
Thermostat:
https://amzn.to/3a6mlnU
how big is your greenhouse anyway?