If they're the same ones I'm thinking of, I got me some of those Spitfires last year. They set me back about €2,50 a piece at Action in the Netherlands and are quite good for what you pay for!
I'll check out a shop again to see if they are also carrying those tanks now. No immediate use yet, but you never know when they'll come in handy.

But tanks at roughly 28mm will be quite huge compared to a Spitfire, so I suppose the boxes will be bigger?