Hopefully this isn't against the rules as it may fall under "opinion" more than a concrete answer, but I'll ask anyway.
I live near Boston and it gets cold here. My Ender 3 Pro is out in a detached garage with no heat and I'm pretty sure the garage getting down to about -12 °C (10 °F) has ruined a few prints for me. Also I'd love to print in ABS at home as well and I think I'd need an enclosure for that.
Now, the printer technically already has an enclosure. It's in a box made out of plywood with some clear acrylic doors on the front, but I think the box itself has too much extra room and doesn't retain heat well enough (thin plywood?).
So my question is, for anyone with experience printing in cold environments, what are some cheap/easy ways to keep the enclosure warm, preferably as safe as possible since I can't always watch the print. I have a small space heater in the garage but I turned it off last night because I wasn't sure how safe it'd be overnight and didn't want to start a fire.
Thoughts on stuff like "reflectix" liners for the enclosure that would help retain heat, small heaters, IR lamps, etc...? All preferably on the cheap side.