I installed a 10,000 BTU portable in my bus. Air circulation is defiantly a must to keep the hole bus cool. I vented it out the floor so the hot air it generates wasn't blowing on us outside the bus where we sit and have drinks so through the floor was ideal. Both my wife and i are 6'1 so saving the headroom was the reasoning behind not using a roof mount units. Not to mention it was a few hundred cheaper so i can use that money i saved to put into a new fridge
. Its not as cold as my house A/C but it is more than acceptable.