Installing window unit a\c in slideout window ?

I'd suggest a portable unit that has pipes that go through the window or you could use a hole saw (prefered). That way the weight stays in the house and the floor rather than a thin wall/window. Not that expensive by comparison to the rooftop unit. Buy the 2 pipe system (more money) but it is so much more effecient as the cooling air for the compressor is taken from outside and the cool air in the rv is the same all the time. No need to cool outside air over and over again.