To keep the ignition lock from engaging while your van is being towed,
simply leave the key at the indent between off and "run".  This keeps the
ignition turned off but disables the ignition lock.

I have towed various vans for many thousands of miles this way using my tow
bar behind a variety of tow vehicles.

BTW, the extra braking system is a wonderful safety feature that you will
appreciate both downgrade and any time you are forced into an emergency
stop.

Budd Premack
88 Wolfsburg, 86 Syncro, etc
Land of Sky-Blue (Frozen) Waters
Minneapolis, MN