There are some factors that contribute to a van's rollover probability that you can control:
In what condition is your suspension? If you have worn out shocks, or worse yet worn out bushings which contributes to misalignment of your front end, your chances of roll over increase by quite a bit.
Do you have a high-top? Top heavy vans increase the roll over risk. If you have a roof rack ontop of that high top that's chocked full of stuff..., its even worse.
How do you distribute the weight inside your van? Is all your "stuff" stowed away as low as possible in your van and distributed evenly front to rear? I'd rather under-steer then over-steer... If you go into over-steer top heavy while in an emergency maneuver... Yeah your going turtle.
Are your tires in good condition, of appropriate load range for the weight you carry, and properly inflated? If your running around with 2600lbs worth of your "stuff" in the back of your 1/2 ton van using only SL range tires dated 2008 that's inflated to 60psi.. Your asking for it.....
Are you a defensive driver? This is the most important factor. Are you the kind of driver that tail gates everyone and always switches lane to lane that are going faster? Or are you the kind of driver that rarely goes beyond the speed limit in the SLOW LANE and always leaves 4, to 5 car lengths to the car in front of you regardless of speed? Are you the kind of driver who sees a "40mph next curve" sign and ACTUALLY FOLLOW IT?
There are of course things you can't control.. Other drivers, road conditions, weather, the deer that dashes out in front of you while your doing 45mph in a rain storm....