My first winter with xtreme heater on my inboard which gave me a total sense of comfort on keeping my boat protected!
I used the medium heater for a mid-sized (and moderately insulated) engine compartment, and it successfully kept the engine and components from freezing, even during -10 degree F cold snaps. Incredible! I did not want to winterize the engine and fresh water system and not be able to use the boat all winter, so this was a perfect solution. Very well built and reliable. Buy the mount too -- allows for easy removal for spring, or easier installation overall if you're leaving in in permanently.
Pro tip -- if your dock power isn't entirely reliable and you're using the unit as described (to protect an unwinterized engine), I would encourage the installation of a power or temperature monitor. For us, the combo of Victron Cerbo (with temp sensor), BMV 712 battery monitor and 4G LTE Modem (cheap IOT sim card) give us remote alarms when the dock power is lost. I haven't seen temps in the engine room below the mid 40's with the heater installed -- usually hovering at about 48 degrees F.
I use my heater in my 1970 VW bus to get it to start up in the mornings. After I installed the Xtreme Heater in the engine compartemnt, the bus starts up every time.
The xtreme heater has given me the ability to ride all year round with the confidence that my boat is protected from the elements. It successfully protected my Malibu Wakesetter VLX through historically low temperatures and one of the worst winters on record. I am convinced that the Xtreme Heater is the most cost-effective, reliable, safe, and easy to use product on the market.
It makes our life really easy and has protected our valuable investment!