We've hauled our tandem inside 4 different minivans without trouble. In all cases she goes in bass-ackwards. Back wheel up front between 1st row seats. Here they are:
1991 Oldsmobile Silhouette - remove one or two 3rd row seats, pull tandem front wheel
2002 Toyota Sienna - also remove one or both 3rd row seats, pull tandem front wheel, or turn to side
2007 Honda Odyssey - flip down one 3rd row seat, remove 2nd row console/jumpseat
2011 Honda Odyssey - flip down one 3rd row seat, remove 2nd row jumpseat
We bought our first minivan used from my grandparents to haul our dogs and the tandem... And we never looked back. Minivans are just too darn useful and far more space and fuel efficient than an SUV. Oh, and rolling the tandem inside is a heck of a lot easier than putting it on a roof rack (been there, done that with a couple of different cars.)