Yes, the 37s probably won't fit well over the 32s, but contact Riv to
make sure the Amos can take 45s, which it may not! Plastic fenders,
which I no longer prefer, do have the advantage of fitting over bigger
tires as they don't have rolled edges. So if the 45s don't fit, you
may have to go with a 40mm or so plastic.
Gernot