A cheaper substitute than the pre-made ones can be aluminum J channel you can find in any home store (Lowes, Home Depot, etc.). You'll have to cut the long leg a bit, but that can be done with a straight edge and a box cutter, followed by a coat of black spray paint. This solution is a LOT larger and than the mini guttering they sell for RV's but I'm going to try that solution on my Bus to catch water that comes under our 2 big Paramount awnings. Carefree recommends one square inch cross section one inch deep, and that's quite a bit bigger than the factory gutter on the Bus.
2013 Tiffin Allegro Bus 43QGP
2011 Chevy Silverado 1500 Toad