Lots of good advice here..
My biggest issue with pulling any kind of TT with a Van is the Front wheel drive. Even with a Weight Distributing hitch there will still be more weight on the rear axle as the front, thereby lifting said front higher and thus less traction.
I cannot count the number of times i have seen "accidents" waiting to happen when on the road in the summertime. Mini Van loaded with kids and gear + a pair of bicycles on the rear and a 19-23'ft TT attached. Looking at these rigs from the side...they look like a V. SCARY.
Pure madness in my opinion.
Van + Tent Trailer or Pop up as my 'merican cousins call it...is the only way to go...as the kids get older/you get larger vehicle, then you can consider going with a Hybrid (they are awesome), or 24-27' std TT and later on yet, when said kids no longer come camping with mom n dad, buy the TT or 5th of your choice towable with a 2500 HD type truck. (go diesel)
Look around for used. There are literally thousands of trailers out there and most really get little use.
As noted previously in this thread...mileage will suffer greatly regardless of Tow Vehicle. It's that giant sail you are pulling through the wind that does it.
If you are in fact going to tow anything with a Mini-Van..make sure you put a auxilliary transmission cooler in that van. $ 350 well worth spent.
rgds from the great white north.
Stk