I'm sure this has been mentioned, but I couldn't find it anywhere so I figured I would bring it up just incase.
Many of the new HD tanks that Wargaming are introducing have invisible parts to them. For example the Lowe, IS-7, JPanther, Panther 88 have invisible hulls. The Centurion 7/1 has an invisible turret, and the M4 Sherman has invisible suspension.
I'm not sure if its a texture thing or if its a polygon thing. To be honest I have no idea what would be causing it but I read somewhere that turning off GSLS would help, though i'm not sure how to do that for this game as it is separated from the rest of the code weavers games (as far as I know) so the little registry editor isn't even on the computer.