I have no recent experience with Tamiya paints, it is twenty years since I used them. I had problems getting it to cover Humbrol spray paints, and it did not seem to like the white metals of that time.
Vallejo covers nicely even if you apply it to plastic without an undercoat.
I normally use Citadel Chaos Black spray as an undercoat. For my British tanks, including an out of place M4A3, I used PSC British Tank green (the nearest Vallejo colour is Russian Uniform).
When I get round to the Yugoslav film star, I will use Chaos Black spray followed by US Olive Drab.
Have a look at Google results for "vallejo us tank paint".