If you have a roofvent with a fan, running that with just the rear side windows cracked will move air through the van and remove heat well- this works when the van is parked on a hot day.
there are screen kits- or Shannon and I adapted a couple of the as seen on tv screen kits with added magnets for our side door, rear doors and front windows- total cost $34
( we have a pleasure-way- built on a chev)
ADCO makes windshield/ door window covers- there is one version in which there are screened portions - these are not meant to be bug proof but work fairly well- adding magnets for a better seal helps
unless it is really hot, we don;t much use the AC
mike