We just went through a W/D installation in a fifth wheel with the W/D closet and prep in the far right front (curb side) of the trailer. Water and electric were prepped but the location where the manufacturer had placed the decal for the vent hole would not work. The washer would be right up against that spot on the wall when installed not allowing any space for the vent hose. The techs who did the installation removed the front wall of the W/D closet (up against the front cap), modified that wall panel to route the vent hose, and cut the hole through the side wall a bit higher and farther forward than the manufacturer's decal would have had it. It looks very nice on the outside, too.
As for ventless dryers, we didn't even consider them. The condensation drying process is slow and inefficient. Our regular vented dryer works very well.
Rob