I've poured a slab and bought coping for one.
The slab spalled, but is a huge pain. Mine was rebar reinforced and you have to pour it off the ground because you'll need to vibrate the hell out of it. You should also use 6,000+ PSI concrete. Mine was 16" wide, 2 inches thick, and 8 feet long and likely weighed 300-400lb.
After that thing didn't work I ordered some high strength pool tiles. Each one weighs about 75lbs. You have to put backer board on top of the box and mortar them on there. I used concrete densifier and the box has those heavy duty toolbox casters. It has still chipped and I had to use a concrete sanding wheel to make the side more rounded. So far it hasn't been remotely with the effort.