Yesterday we were running through high 80's low 90's with just the engine AC. With two forward slideouts their forward walls close 2/3 of the space behind the driving area and seem to contain the AC just fine. Pity anyone riding further back in the coach without gen and roof AC. That is what they are for.
I saw the statement about engine AC costing more than roof air to operate, I have never seen it proven. Certainly on some of the hills we would have been better off with the engine AC off, but that was only going up hill.