We usually use magnets to mount cameras, including on the grain cart. Photo shows our Cab-cam mounted on the side of a Brent cart. I use the round chrome-plated type magnets. They're rated at around 90# pull. Been using them for a few yrs now. Never-ever have had a magnet let go. I use a 3/16" bolt to secure the cam bracket to the magnet. Make sure to put the head of the bolt in the center of the magnet so that bolt will not accidentally protrude & hold magnet away.

We also use ram mounts for other things. I'd also consider using a ram mount bolted to a magnet. That would work fine using the "short" ram arms.

You'll note in this photo we also have an extra light on the side of the cart (besides the standard auger light) that's also mounted by magnet. It all works fine "here".