Yes, your carvan does have a cabin air filter, its on passager side under the ac case. can't tell you how because it is a long to put at this web site. most all parts houses sell them, sometimes thay can tell you how to remove it.
Most Caravans I have seen don't have the cabin filter. The air handler under the dash on the passenger side is molded for one but it was never installed. I tried to install one in mine. I cut out the opening for the filer and purchased the filter door for $6 from the dealer but the filter needs a track to ride in or it just flops around and would not be affective. The dealer only sells the filter door and the filter. I found a Caravan with a cabin filter in the salvage yard but the filter tract wouldn't come out without damaging it and the salvage yard wanted me to buy the whole unit. At some point I will make a track out of channel plastic and seal it up as good as I can but in the end if yours didn't come with one it's not worth the hassle to put one in.