What I have used the last four years is Home Depot and Lowes have a oil filled radiator thats electric for $39-49. I keep one on all winter so temp is about 70 If painting over night the heater will have it at 85+ next morning.
I have them both running when I'm painting.
Best part is cheap to run, I have a separate meter on paint garage and cost me about $25-35
a month. It so efficient and with Natural gas going up last year bought two more and put in basement figuring it would cut back on my house heat bill. Don't know if it helped or not! Duh!