When I see spots with a plug it usually means 1 outlet goes for each spot on either side.
Anyway, try one of these (or Canadian Tire special): https://www.amazon.ca/Fosmon-Outdoor-Mechanical-Resistance-Grounded/dp/B07F7GD3CD/ref=asc_df_B07F7GD3CD/?tag=googlemobshop-20&linkCode=df0&hvadid=293011570232&hvpos=&hvnetw=g&hvrand=13440175498494024161&hvpone=&hvptwo=&...
Says it's can do block heaters
-Ron Wharton