I really like toilet paper rolls as material.
These look so real, I was asked if I was working on my car's muffler when I made these.
The key is the rust effect paint job.
Apply sand mixed with PVA in a random fashion, then undercoat black.
Paint the whole thing silver, pick out the sandy parts by drybrushing, bring them up from a dark brown to a glowing orange, tone back down with lots of black wash, apply silver and orange drybrush again where it's needed.