When tailgaiting or running extended period of time without moving, we always us our homemade genturi type exhaust. When using generator while traveling, we've not had any issues with fumes. I did add an extra CO detector inside MH right where exhaust exits under side.
I do not agree with rockhillmanor's posted issues with a Genturi. I used EMT elbows for the metal part that connects to generator exhaust and 3" thin wall PVC for the "stack." After running generator several hours, the PVC only gets warm to the touch...not hot. Also, I bent some pieces of aluminum to mount the PVC to metal elbow just like the genturi pictured so cool air will be pulled into the PVC and no back pressure on generator exhaust.
If you are able to make one ***PROPERLY*** then DIY is just as safe and cost way less than purchasing one. If you don't have tools/skills/etc. to make one properly, then YES you should buy one..