I´ve rented out (other) vehicles and props to TV and movie productions numerous times. My main advice: Never, ever, rent it out without you being present all the time. Or better, bring a buddy with you so you can go to the bathroom while the other is watching the vehicle.
Otherwise, the prop department will do with your Humvee as they see fit: Drill a few holes for a camera rig, repaint the vehicle, etc.. Or the director will decide to spice up the action sequence with more crashes at your expense.
And forget about any insurance they promise. Even if you get that in written, afterwards you´ll be fighting with an unwilling insurance company working for a not longer existent production company. So: Better be close to your vehicle all the time.
Since the daily rate then needs to replace your daily income, plus that of your buddy, and cover any wear and tear on your Humvee, $ 500 doesn´t look much. Obviously, rental rates will be different depending on location, but overhere, daily rates for a Humvee would have been considerably higher than $500. Plus, vehicle transport, travel, hotel and food would be extra.
Admittedly, daily rates seem to drop overhere, however, since more and more inexperienced Humvee owners offer their vehicles on "movie car agency" sites at far too low prices. Some production companies prefer to work with the pros they know, and pay more; other companies just go for the cheapest offer, and just wear out another newbie.
Personally, I´m not going to go cheap. TV or movie work is not as much fun as you would think, and time in my real job is precious. I´ve been burned by one or two production companies over the years, so am very careful now.