But hey, the cast iron trench armor is still a possibility, right? :|
Uhhhhh. Trench armor, possibly. Cast iron? Probably not, since it's a real pain in the ass to keep unrusted, and it'd be too heavy and obscenely expensive for something as simple and silly as an airsoft tank. The heaviest "armor" I would go with is probably plywood around a steel frame, since plywood is cheap, far easier to work with, and doesn't rust. I'm protecting the crew from BBs, not (real) HEAT rounds.
Oh, I mean, the iron stuff the Germans used in WWI didn't exactly stop HEAT rounds. Hell, it was really only for gunner crews, and most of the time they didn't wear it anyways.
They found it could only really stop handgun bullets. Rifle rounds would usually punch right through. I only really said it for historical comedy's sake