We are staunch advocates of using zip ties to install fenders, at least the plastic ESGEs we prefer and stock. They go on easily and come off easily with a snip.
Zip ties are light, cheap, and a make the whole process much easier.
Zip ties don't work on aluminum fenders, or at least won't last - the aluminum will cut through them at some point. Here's how to attach the fenders without using any bolts at the rear. Put the strut approximately where you would put it if you were using a bolt, then wrap the zip tie between bolt hole and dropout window. The hex wrench is for tightening the bolts that hold the struts in position. Heron with complete fender installation.