Kurts' right, it just takes some work. I slide the wheel pant on, then the first collar, hold that up on the axle so there is just enough room to slide the wheel in, then the last collar after the wheel is on. Using needle nose pliars to hold the last collar helps you get it into the axle, or, balance it on the wheel when you slide the wheel in, and use the needle nose to center it in the axle - dont tighten any collars until the whole assembly is on the axle. Its a pita. I fly off grass, and my wheel pants lasted about 20 flights before they fell apart, you might want to consider leaving them off, they are only cosmetic.
The CA hinges suck. I've read the odd post about folks that have had them work on all kinds of airplanes. I read and exactly duplicated the "method" for installing them, and still they cracked after a short time. Yes they are easy to install now, but later <when> you have to replace them, you'll wish you had used the robart hinge points to begin with.

Roger