Well it's definitely winter again... and at the risk of repeating some stuff, I'm going to post a link to the specific post where I outlined the process I went through to 'winterize' my Emonda. Here it is: The Wet Emonda
Over the years, I've used everything... C-clips, P-clips, a lot of duct tape, brazed on eyelets (which need screws that corrode and rattle and are finicky to install and catch on things). And being in the Pacific Northwest you get to see all kinds of MacGyver'd solutions. My latest incarnation is my best, and so far I have not found a single fault to it. And it involves zip ties. Yup, chuck all the heavy hardware, cut it off, zip ties are the answer for a fendered winter road bike that actually is a proper "road bike". Not a cross bike (been there done that), not a toruing bike with eyelets everywhere, but a proper handling road bike which could be race ready in the summer if you choose it to be. But yes, you do need some MacGyver in you, but to be honest, I've never seen a proper road bike with a decent full fender install that didn't involve some MacGyvering. So, as a preview to the post I linked above, here's a few teasers... also @Bilwit in particular (in reference to a pic you shared of your rear bridge setup on you BMC), and anyone else who is having trouble keeping the fender high enough at the brake bridge (often the tightest spot on a road bike to get a fender past), I did notice that you could get way more clearance if you did away with the slotted tab on the fender that is held to the bridge by a bolt and just used the method below. With riding, it's rare that the bolt that holds that tab tight enough stays tight enogh for long. Those of you who have mounted it that way know what I mean I'm sure.
And I also dont' think there is a thing wrong with using Di2 on you winter bike. In fact, why should you even compromise anything on your winter bike, with the exception of having to add full fenders, and flaps. Just because it's a "winter" bike, doesn't mean you have to run crappy stuff... where's the fun in that. All that does is make you long for the days when you can ride your "good" bike. They can all be good. But I do agree that if it's not fendered up fully, then even though you may ride it in the winter, it is definitely NOT a winter bike by anyone's standards who has ridden for months in a wet/cold climate.
Anyway, here's a couple teaser pics of my install. For more, and detailed commentary, see the post I linked to above...
I know some of you are probably thinking... "Zip ties?... please", but really, the key is prewrapping the stays with about 6 rounds of thick electrical tape (color matched to your bike of course). This completely protects your frame and once you reef down on the zip ties, causes the fender stays to "bite" in and they really don't move, at all. For removal, it's easy... snip snip and they're off. To put on again, just cut a new zip tie and rivet it to the holes that you made in the fenders during the first install. I describe it all I think in the post, which I'll link to again right here... The Wet Emonda
Oh, and I knew there was another "winterizing" thread that I posted to before as well. Just found it...Another winterizing thread
Good luck and happy riding in the rain... well, as happy as one can be.