[McGillicuddy]

Yeah, the bottoms are inside the wheels and some flat steel or alum can be shaped to attach the plastic quarter tubs to the trailer frame.

These barrel tubs are typically only 24" in diameter so they may need to be massaged for a sexier ghetto look and fit, as tires are probably 24" tall on a 13" wheel and 26" on a 14" wheel. Use a heat gun or blow drier with some strategic kerfing to flare the tub out for better wheel coverage. I'll try to make you a sketch tomorrow.

Most fenders are about 9.5" wide, 10-12" just gives some wiggle room for error or less bend on mounting bracket