According to code exhaust can't exit beneath a slideout for obvious safey reasons. When I was at Newmar doing the review for FMCA Magazine I noticed that they ducted their hydronic heat exhaust (they used Oasis, rather than AquaHot) out into the patio area between the bedroom and front slides. When I asked about that they told me they can't let it exit out the driverside due to the full wall slide.
Also, Newell does not exit out the roof. Newell has dual exhaust diffusers at the rear of the coach, a remnant of the Detroit 60 series days. They only use the right side for the Cummins ISX so they duct their generator and AquaHot exhaust out into the left diffuser. When at American Coach I noticed that they route their AquaHot exhaust out the back as well, using a separate tailpipe. All those bends were approved by AquaHot and in my opinion it's the best answer because it doesn't impact the patio area or your neighbor's patio area. Plus, you can leave a roof vent cracked open a bit without fear of an exhaust backdraft wafting back down into the coach, unlike a Bluebird Wanderlodge with the roof stack.