Ok , here's a drawing for the fixed window (s) ... Agree with the need for ventilation ... Got a standard top vent for mine ... Easy to put screened vents in the floor too ... and if you use a hole saw , you'll have the plug too ... for traveling in wet weather... or use the smaller deck hatches ... like Todah suggested... even in the rain , if you have e vent in the floor and the top vent cracked open slightly (enough to keep the rain out ) the hot air will leave from the top, the cool air coming in through the floor ... We did floor vents on Kustom Vans back in the late 70's ... a much appreciated option down the road...
For a deck vent , a few of these http://www.amazon.com/Tempress-Products ... 177&sr=1-3 in the floor would allow venting , and access for an electrical cord too ... I am planning on a 50' GFI extension cord as my electrical system ... with a bottom hole , I wouldn't have to put a hole in the wall for access, no shore power fixture $$... or a hole in the door for access, that might leak water inside in the rain ... You could just staple some screen on the underside if you wanted ... easy !!!