You're in a very good position. Most Brits 'wintering' in the US have to worry about not becoming resident for tax purposes by staying too long, and going through the hassle of filing the form establishing 'a closer nexus(?)' to the UK. You're a US citizen so you'll always have to file a US return.
On the other hand, you have no 'earned income' and will always have to use form 1116 (FTC) for your US tax return. That does away with the need to establish the PPT or Bona Fide residence test for 2555. A CAVEAT: nonetheless, you need to be sure that the US, and State, are happy you are indeed resident abroad (8938, for example) and not resident in the US, so you must be careful not to spend too much time in the US. I don't know if this would fall under the substantial presence test, or what, but it is something to be certain of before your first extended trip back to the US.