I have a 2001 Grand Caravan adapted by Rollx (www.rollxvans.com.)  There
are other companies that do conversions, also.  The only structural
problem I had was that heavy duty load adjusting shocks weren't installed,
and the bottom of the van scraped going into and out of my driveway -
installation of Monroe SensaTrac heavy duty Load Adjusting shocks solved
that.  I believe those shocks may be standard on Rollx conversions now,
but I'm not sure about that.

Two great sites to find more info on Caravan conversions, and other
mobility info are:

www.wheelchairjunkies.com - where I found out about the shocks issue (Mark
Smith, the site owner, really knows his stuff, and the message boards are
a big help.

www.carecure.org - the Care-Cure forums.  Best spinal cord injury site on
the web, IMO, but also a good source of info for wheelchair users who
aren't SCI in the Equipment forum.

I hope these sites help.

Alan