FT in the DA isn't what folks want. There's a reason the other arenas are basically empty. It's the comraderie, the banter, etc., etc. or the "social aspect" if you will.
How would Tank Town do if it was purely in the DA? Is that what the tankers want? I doubt it.
As for an idea for FT Trinity... JUST an idea for Trinity... why not another "ring" of mountains. The tankers have the innermost "basin" or "bowl" to battle in, surrounded by your high mountains to keep the nasty old aircraft away, pretty much like it is now.
Then ANOTHER ring of mountains surrounding TT with a few bases in it owned by each country. Between these two rings of mountains, let the furballs roll.
Each country would have fields in both places, each country would have equal access to the two inner rings.
Just a thought.