Thank you for sharing this. I'm going to buy it the next time I come home with a truck coated below with mud and sand. This will be way better than lying on the ground.If you have a pressure washer one of these is what I use to get the underside clean. Not as good as being able to get a direct nozzle on specific areas but will clean most of the crud or salt off.
https://www.amazon.com/MINGLE-Pressure-Washer-Undercarriage-Cleaner/dp/B07RZYSL1Q/ref=sr_1_5