I've added these to A/C's and they work well. Most A/C's are equipped with a plug and play connector inside. You can pull your inlet vent cover and see the metal control box inside. There most likely is an extra connector with nothing connected, designed for an add on heating element. Such as in this link:
https://www.amazon.com/dometic-heat-...tic+heat+strip
Just match your model to the correct element. Not too hard to install if you are handy, you need to pull the top off the A/C. Is only about an hour labor time for a Tech at an RV shop to do it for you.