Got an E-Z Heater from Aircraft Spruce.
A less expensive route would be to use a [URL="https://www.napaonline.com/napa/en/search/?text=heater%20pad&isProduct=true&isInterchange=true&referer=search_form-allprod"]NAPA heater like Randy Lervold did on his RV-3[/URL]. Website says he used a 50W version. I would pick a 150W version like my E-Z heater that warms up my Lycoming engine in Pennsylvania with 2-hours of operation before flight.
Amazon even has a pad heater. The E-Z heat has a three prong plug and the images of the others do not. Not sure if it is worth an extra $100 US for the three prong plug.
Do not forget the SwitchBox Control so that you can turn it on remotely from the warmth of your home.
I use hair dryers donated by lady friends. One in each nostril and sealed with drywall sponge. Heats entire engine from 30 to 75 degrees in 40 minutes.
One or two 75W light bulbs in cages plus blanket over cowl works great. Heats up entire engine in a couple hours.
I've been using a hair dryer as well and with a 4' section of scat tubing attached to it. Works well and super cheap.