ok, so even dvd drive, I'm not sure what you mean by how thick the plastic is around it? the thickness of the tiny plastic lid that sits at the end of the tray installed to make it flush with laptop's surface for aesthetics? well, I could check exactly once I get home, but those are not too thick 3-5mm maybe, since they aren't meant to provide any structural support in the chassis.
as perfectblue says, I'm surprised to see you find MSI case to be not durable. The gaming series laptops like MSI, Asus and Sager I've found all of them to be one of the sturdiest constructions.
best advice I can give, try to watch some videos on xoticpc website, they have them for every laptop they sell, perhaps that will give you a better idea of durability. Or try to find somewhere in your neighborhood a store that carries Clevo cases