Pushing the boundaries for clearance makes fender installation - both plastic & metal - challenging. I find it's always a lot easier to live with a tire one size down from the max. spec. They are easier to set up and have more forgiveness for any possible shifts while in use. Also, the extra space provides less chance from damage caused by jamming a stick or pine cone into them.
Pat's Betty( the Riv Demo) came with Fatty Rumpkins and the Longboard fenders. Getting them set up was a bear because the clearances were so small. The tires measured 41 mm wide but appeared to be rather tall. When we were re-prepping the bike this Spring, I again found myself struggling to make the combination work. I eventually decided it wasn't worth the effort and gave her the pair of 38s, in this case Pari-Motos, from my Saluki. We ride pretty much entirely on country roads & car free paths so have little concern about flats.
I found that the Rumkins would fit under the VO Zeplin fenders on my Saluki. It was tight, but not as tight as the Longboards. But I decided those tires were too stiff for me and bought a new pair of 38s.
If I were you I would buy the VO Zeplin fenders and an appropriate set of 38's. If you're touring and the bike gets knocked over or banged at a rack the fenders can get out of alignment. There is much less chance of that with metal fenders and if it does happen you probably wont even notice with the Al. fenders & 38 mm tires.
Yes, they are more work to install, but if you are patient and relaxed, I'm sure you can do it.
Is this your first pair of fenders? I have only found two negatives about fenders. They can make many poorly designed bike racks nearly impossible to use. They are not compatible with many styles of car carriers. If you use a fork mount you will need an uplift and still be careful about how low you can put the fenders. I ended up installing the fenders on my tandem three times before they were high enough to clear the carrier. Also, some roof top and hitch carriers which grab the front tire look like they will not play nicely with fenders.
Michael