You don't say how big your stall heaters are. If they are hard wired 240v, I use these on our well pump and water heater. I really like them because we have a scene that shuts everything down when I leave my cabin, but I can monitor power draw on each appliance that they are on: https://www.amazon.com/dp/B00MBIRF5W/ref=cm_sw_em_r_mt_dp_Ok.ZFbD3AE5WQ?_encoding=UTF8&psc=1

For less than 15a space heaters, I use dongles like these (aotec or zoos, I have several). They both switch up to 15a and have real time power monitoring. It's nice for space heaters, because a switch just tells you if it's on. The power metering tells you if it's actually heating. At least in a Vera, there are plug ins that will log the usage and you can tell if it never shuts off, etc. https://www.amazon.com/dp/B07578W7KY/ref=cm_sw_em_r_mt_dp_uk.ZFbSR0JY4P These are only rated for dry areas/inside though. I do use them in unheated garages, but not exposed to elements.

You can also get low voltage/current relays and just use them to trigger contactors for large loads, but you usually lose load monitoring on those.

I use this guy for that exact scenario.