I did have a HUGE problem mounting them. It ended up taking me several days, using successively larger tubes to form the tires.
Apparently there is a much better procedure, that was sent to me from Chris from Challenge. It follows below:
Due to the construction of our handmade open tubulars, they tend to lay flat and tight on the rim. Once installed and a tube inflated, they take their shape and stretch a little making future removal and installation easier. It’s that first installation that can be a real pain depending on the rim.
Working with the folks in our factory we found another method for installing these tires. Rather than pushing everything on from one side, as is traditional, follow these steps:
5) Install the remaining side of the tire
We’ve found this to help immensely with tighter fitting tires like our handmade open tubular tires.
Doing it that way should help you hurry up and get out the door in order to start doing some of this: