The property which I bought, the guy who'd bought it before me, he had lived on the property for I believe it was about 3-4 years. Then, he had to leave the property for a few years, and things just grew-and-grew, where we'd not prefer. But, before he'd taken off for that vacant few years, he'd had a pallet of 40# concrete bags delivered, and that had gotten left laying in the grass.
That pallet pile of those concrete bags, then turned into a bunch of big concrete 'bricks' by rain. Those could then be used as big nice uniform 'rocks'.
If you cannot currently afford a proper concrete pad to be built, see if you could lay out a 'somewhat smooth' pile of those concrete bags, get them wet and cured to become some big 'bricks' for you.
Then you can set your items on top of the 'bricks', keeping them technically a bit up and out of the dirt. You can just trim around the bit of weeds that may grow, much easier than if they're just laying on the ground.
It's not the most attractive solution, but it may be a better peace of mind, knowing you're not constantly putting a bunch of undesired chemicals on your ground.