It sounds like you have done everything you can to take care of and maintain
the vehicle.  I would think that the chances of you having head problems are
much less than someone who didn't pay as much attention to thier van.  However
anything can happen and since Murphy's Law always seems to kick in at an
inoppurtune time I would suggest taking a bottle of ceramic Block Sealer on
the trip with you.  Put it in the glove box just in case.  It only costs $14
and its cheap insurance.  If you get head leaks on the road just get the van
taken to a shop or stop somewhere with water available and use the sealant.
The next day you can drive away and should have no more head leaks for the
remainder of your trip and for some time to come.
This is just my thought.  Also carry a couple spare gallons of coolant/water
under the rear seat just in case.
Have fun and I hope that you never have to open that bottle.
Ken Wilford
John 3:16