Hello. Welcome to Just Answer.
There is no Code against using 2 levels of GFI protection on one circuit, even though it's really not necessary.
If both breakers hold, and you don't get nuisance tripping from either one, I see no reason not to use it.
However, you very well could experience tripping issues with GFI protection on both breakers.
The good thing about this is that standard double pole breakers aren't very expensive.
OK. So to install the GFCI at the source panel, I would use the same wiring as the GFCI in the sub-panel? i.e. red, black, and white to breaker, ground wire to ground bar, and white coiled wire from breaker to neutral bar?
Yes, that's a good explanation.
You are most welcome. Is there anything else I can do for you?
one more clarification....the white coiled wire from the breaker must go to the 'neutral' not the 'ground' bar, correct?
Yes, that's correct.
My pleasure. Have a great day!