Thanks, gentlemen!

The rusted plate is AK rust effect paints stippled on in various layers, then some Vallejo liquid mask stippled on around the edges, & a mix of Tamiya XF-1 & XF-69 similar to that used for the lower hull, thinned out quite significantly (1:2-ish) with IPA, sprayed in thin layers until I was satisfied with the depth of colour (which still allows a bit of the rust colours to show through), &, finally, removing the liquid mask by rubbing with a ball of old liquid mask & tapping with masking tape to leave the exposed "rust" areas.
The quad turret is painted SMS "Light Green G5" (British WWII AFV), as is the shield & mount for the Mk.19
[Note: I'm mentioning all the paints for my own reference later, should I want to replicate something like this again, or do any touch-ups.

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