if you want to put weathering on tanks, here is the process i follow:
1) Paint tank flat colour
2) Wash the tank with 'nuln oil', with patches of 'chestnut ink'
3) Dab with tissue
4) Highlight the edges with original colour
5) Use 'rhinox hide' and a sponge, and dab it over the tank. Thicker on places that accumulate rust.
6) paint black chips along edges, and then fill in with grey (not boltgun metal) to make paint chips.
7) final patchy wash of 'ogryn flesh'
That makes you tanks look really crapy, rusty and beaten up - if that is the look you want. If you want them to look new, you still need to wash them as the paint colour as it stands is far too flat and unrealistic I think.
Sorry to be punchy, I like the tanks, but I think they need to look dirtier.