We prefer our tandem inside and not on a rack.
Back in the 1970s we hauled our tandem inside a VW Squareback with the hatch part way open.
Have carried tandem inside Honda Accord Harchback with hatch part way open and inside our current '97 Honda Station Wagon with both wheels on with hatch part way open. Or, for longer hauls, we remove both wheels and shut the hatch.
Actually a tandem will it inside a Honda Fit!
We own only one vehicle and have only one driver so no need for 2nd car or a dedicated tandem hauler.
Where there's a will, there's a way.