Often, in your situation, you just need to get the exhaust a few feet from the side of the RV to solve the issue. If that's the case and you rarely need to use it, just go to Home Depot and buy a 36" or 48" length of the flexible water heater vent tubing. You can then just lay it over the end of the exhaust and use a stake or other support to direct it away form the RV. The diameter is large enough that you won't case any back pressure.
If you plan on doing this a lot, buy the Genturi. Whenever my coach needs repair or some item added, I enjoy doing the work and fabricating whatever it might need. Even though I like making stuff that is usually better than what I can buy, the Genturi is probably one item you should just buy from the manufacturer. I know many make their own, but what's your time worth. The Genturi comes on sale at Camping World all the time for about $110.00. The quality of the Genturi piping, carrying bag and premade elbows is hard to beat, and is nice looking.
Don & Mary
2014 Newmar Dutch Star - All Electric - 450 ISL
2016 GMC Canyon 4WD Crew Cab