In my experience, I would avoid writing trade/gift on the purchase amount. This worked a few times in the past but more recently, they have asked what the value of the trade was and/or write that in the purchase amount. I never tried the gift method but they may tax you for the entire amount on the Escape. If the plates on the van were registered to your or your wife's name, you can reuse them for a little bit of credit. I recently had to jump through some hoops on a motorcycle title that was from MO and had to talk to the DMV many times on the phone. Oddly enough, they were pretty helpful with answering my questions. It may warrant a call to them and ask them what you 'should' do but I wouldn't use the term "cheapest way" for obvious reasons.
As always, you should always be truthful in these types of scenarios because Uncle Sam deserves his cut out of everything, even if it is something that cost you nothing..