For such a large area, we like to use the Big Green Sucker drying towel and our Boss Gloss with it. Boss Gloss functions as a drying aid in the Big Green Sucker, helping it absorb water more readily (slightly damp microfibre absorbs water much faster than dry), it also lubricates the towel to help minimize any errant dirt or dust from scratching the paint. For larger vans, you may need two Big Green Suckers to completely dry it all in one go.
Get The Big Green Sucker and drape it over your arm with the bulk of the towel hanging down. Spray 4-6 sprays of Boss Gloss straight into the towel. Flip the towel over and spray another 4-6 sprays on the other side. Now dry the larger panels of the van as best you can, starting with any windows first to minimize water spotting issues. You'll want to focus on the sections that are in the sun, leaving the ones in the shade till last.
Once most of the flat surfaces are done, grab an electric blower like our 18V Milwaukee here, and holding the cloth nearby, blow out every single crevice, window channel, hatch seal, and any other intricate areas where water likes to hide. This helps eliminate any run marks from appearing after you've finished drying. Make your way around the van until you're happy the bulk of the water is gone.
Give the tow bar a quick blow down as well, then wipe dry with a folded Dirty Deeds cloth sprayed with Boss Gloss, you don't want any leftover dirt from these lower areas getting into your Big Green Sucker and causing scratches!