K1 application where USC is overseas with fiance, no address

[CEG]

US citizen travelling abroad with her fiance - they have no real address presently as they are backpacking around asia - she has a US mailing address and will have mail here checked regularly. He will return to the UK (his country of citizenship) in about 4-5 months when we expect consular processing will start and so we will designate the consulate in London for processing. Is there any chance that the USC will be required to submit biometrics before the I-129F is approved? Being overseas I don't know how she would do this. This is the first marriage for both parties and neither has any criminal record. What do people suggest as listing for a current address for both the petitioner and the beneficiary who are not staying anywhere for more than a few weeks at a time?