I have the same issue and to lock the van without setting the alarm you do the following.
1. With drivers door open press lock button on remote.
2. Press unlock once so driver door only unlocks
3. press down button on drivers door and close door. Not the button for all doors just the slider button.
If you take the van to the dealer they can scan the alarm system to see what is setting it off. They told me to diagnose the alarm your trunk key must work which mine does not. It's seized up.
1999 Chrysler T&C Limited AWD 250,000kms