I painted up GZG’s 15mm fuel drums (type A) the other day. They were easy to paint. I primed them black, dry brushed on some gray, then a smaller dry brush of red-brown for rust.
I based them on some small wood rectangles, then glued some sand on the bases. Then I washed the sand a sepia color, then dry brushed the sand with a tan. When that was all dry, I brushed on some very thin PVA glue-water mix to hold it all together a bit more permanently. The I dry brushed some more tan, as I felt it needed a bit more.
That makes for some cheap and easy terrain.
In the past, I had assembled a card stock “print-and-fold” barrel, and it took a lot of time to cut the small bits out, and gluing such a small thing was tricky. I think these metal barrels we easier, quicker, and much more durable.