Just writing back to post a reference of my ski transport arrangement for my family of 4. Note that the boot bags are not yet in the car in this picture, but they fairly easily fit two on each side.
I don't normally tie the bags down as the ski bag is pretty well wedged in. I'll also not that this isn't probably a good solution for people who baby their skis - I do, after all, have four pairs in a bag 'designed' for two pair...
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