Camping world sells an extension as probably do most RV centers. Mine exhaust out the rear of the unit, so I don't worry about the exhaust fumes. If it exhaust below a window or door, I would definitely get the extension. Welcome to the forum.
is there some easy way to extend the exhaust pipe up on the outside of my motorhome up to the roof of my motorhome with out hurting the generator.
You can make your own exhaust exten. out of 1 1/4" elect. EMT pipe. Cost about $5 for a 10' long piece. You can chose to run it up above roof line or along bottom of RV to the rear, the choice is yours.
If you camp in close to other campers at races or events it would be a good idea to go up over the roof to keep from exhausting on your neighbor. Very dangerous but, I would do as Larry suggested and ck with the manufacturer.
You also might to make sure the pipe clears the top of the rig. For example, my 25ft Class C fleetwood Jam has a vent just 3 feet from the rear, in the middle of the roof. Running my pipe strait up puts it right in line with the vent. If the wind is blowing.. you get the picture. Pluse, make sure your awning is out of the way. Again, a pipe on my unit wouldn't work as the awning extends behind where my gen is (rear of RV, passenger side). I can use 45deg bends but was told this isn't good on the gen for an extended period of time.