Does the heater add-on feature work very well on this A/C unit? I was thinking about ordering the kit; it just plugs in and there is a switch position for the heater. Thanks for any info..

Think of it this way, heat rises and you are installing it in the roof. it works very well for worming your scalp, but the feet are cold. I use a 110v box heater that cost $19.99 and it will keep the trailer worm in 20 deg weather.
The cost of a heat strip is about $175.00 installed. Totaly not worth it.
Sam