Good morning Starider,
I am hoping that most of us have legal reflectors, but, if not, I think your idea of mounting them on mudflaps is fantastic.
I had be worrying where I would fit additional reflectors, if needed.
I had been considering mudflaps anyway as my white paintwork gets very messy behind the front wheel arches on the front doors.
I will also have my mains hookup under the car behind the rear wheel arch (out of sight); another reason for a mudflap.
I have seen some mudflap sets on ebay that purport to be for Alphies, only £14 (or so) !
Thanks again for sharing such a great idea, Good luck with the fitting process.