I would sometimes like to transport my tandem by car, and it would be convenient to use one of those "strap-on" bumper carriers. Is it feasible to use this type of carrier?
Yes, yes it is possible...
If the tandem is loaded onto the carrier at an angle, it won't extend much beyond the width of the car or minivan (maybe not at all for a larger vehicle). It's not totally clear in the following picture, but the horizontal bars are tilted up a bit to make it more secure.
It's necessary to bungee-cord the bike or otherwise secure it otherwise it'll tend to slide "down" (in my case, the front will tip down, which will make it stick out on the driver's side). I use 2 cords to secure it:
- I immobilize the bars so that the wheel doesn't flop while loading/unloading (and while removing the front wheel, which I have to do to keep it from sticking out on the driver's side.
- It's not clear in the picture, but behind our mini-van, the front forks don't stick out at all, and the rear wheel sticks out maybe an inch beyond the width of the van. Also, the bar-ends I have don't stick up above the roof box.
Although it looks ridiculous, the same technique can be used on a small car:
The bike doesn't actually stick out beyond the width of the car as much as it appears to in the picture, it's less than a foot on each side. It does stick way way up above the car, however, so when I've done this (only a couple times) I'm very careful about going into underground parking.
Can you tow a trailer with your car? That would be the safest and most responsible way to move your tandem.
Second option would be to ride it there, over the course of a day with rest stops you and your co-rider could do 100 km.
Another option would be a roof rack, like others have mentioned. Your vehicle's roof looks long enough to accept the full length of the bike. Brands to search for may incluide Thule. Possibly you're looking for three cross bars, and two normal "bike rails" in line-astern or as close to that as possible. May have issues with the front bottom bracket being super low, which means an adapter to raise the front fork a bit more than normal.
Please let us know what you end up doing.