Chevy & GMC Vans

My wife and I are thinking about doing a van/camping road trip in the last half of September,through coastal Washington,Oregon and possibly northern California.We're from way north in Alberta so weknow nothing about what seasonable weather norms to expect.I haven't outfitted my Astro van yet but am wondering if anyone could tell me what kind of weather to expect.Will I need window bug screens,an aux heater,a/c, roof vent? etc.I have a futon that will work as a bed once the back seats are out,have all kinds of camping "gear'" but have never camped in a minivan.I don't want to go wild on modifying the van,I'll be putting the seats back in when we're done,but any camping tips you could offer would be helpful. Thanks!

Heater: No. (But probably a good sleeping bag or blankets)
A/C: Probably not, and not practical anyhow.
Roof Vent: Probably not, especially if you get a screen for the rear.
Bug screens: Yes.

I use these for the front windows:
http://www.theskeeterbeater.com/

I am in the process of making a screen for the rear hatch. In muggy conditions, we do not get quite enough airflow through the van if someone is sleeping in the pop-top bunk (the opening is too small and too close to the front windows to get sufficient airflow. Top-up and nobody in the upper bunk is much more open so the airflow is greatly improved, but that doesn't apply to most folks.

We just returned from 5 weeks in the PNW and northern Rockies. We only used our bug screens a couple of times and to be honest, my experience up there would suggest little in the way of bugs by late September. As for heat, the temps can be pretty variable that time of year as can be the weather. If you have a Mr Heater it might be nice to take; it's nice to have after multiple days of dampness. T.Low would have better info....

BTW, my nettings consist of no-see-um netting cut roughly to size and magnetic strips pulled from old refrigerator doors. I keep the strips in the door jams and fold the netting under the mattress.