[Mikendebbie]

You did not say what year model you have - but looking at the floor plan it appears to be an easy straight shot to go behind the washer/dryer units with the dryer exhaust.

Try this for the heck of it...google "2017 Keystone Montana 3820FK" and you will get lots of advertisements for units for sale at dealerships all across the country. If you click on "videos" then you will get sales videos that generally include a walk around the outside...or just click on some of the units for sale and they will have photos. Look for a shot of the drivers side rear and some of those units will have a dryer exhaust vent and this will give you a general idea where they have been installed in other units. I found the screen shot below in one of the videos and I sketched in the washer dryer units + the way the exhaust goes to the exterior wall.