Good questions and fair points.
In no particular order.
Most builds get done and the builder is busting his or her tail working after that and doesn't post much. Also most folks don't want to come on here and say "oh man I screwed the pooch on my build" and this and this is wrong.So we don't get a lot of after build reports.
I have only been around one system that had ("makeup air") out door air coming inside at the grill front so the system was sucking out the heat and grease from the grill and not the AC, or heat in the winter. It was in the dead of winter and colder than hell outside and as you reached across the grill to turn a burger from your wrist to your elbow was cold I mean frost bite cold. So in my mind they ("makeup air systems") work.
But that said they can get expensive to install, and you need to figure out how much air to bring into your hood area. The only way I know of to do that is get back on the phone with VD and ask them to tell you what system they recommend for your rig.
Tell them you also want to use a make up air system and ask what size pipe etc you need. They can figure it out in a heart beat. And yes they will want to talk mushroom type but you just need the CFM figure that they suggest you need and the CFM "makeup air" figure they suggest you need.Then when you build your system use VD's research, and make sure you get a total coming in and exhaust that matches.
I live in Illinois and we have about two weeks in early to mid August that are just miserable from the heat in a normal year. This year we have had several weeks already and the worst may be yet to come. I do not have AC in the trailer but run the exhaust fan all day to keep air moving thru the trailer. Again under normal conditions it's not bad with out AC.
<message edited by Dr of BBQ on Mon, 07/23/12 3:15 PM>