The only negative I can think of is the heating and cooling could cause some condensation to occur inside your engine. If you are in a dry climate, no problem, but in a wet climate, maybe find another way to load up your genset.
I just ran mine today and used 2 little cube heaters at full whack for around 45 minutes. They draw 24 amps together, so that's around 3,000 watts. A nice load for my 5,500 watt genset.
Another plus for using electric heaters is that they'll dry the air inside while they are running.
Happy Glamping, Norman & Elna. 2008 Winnebago Adventurer 38J, W24, dozens of small thirsty ponies. Retired after 40 years wrenching on trucks! 2010 Ford Ranger toad with bicycles or KLR 650 in the back. Easy to spot an RVer, they always walk around with a screwdriver or wrench in one hand!