This option doesn't work for most but I carry a folding mountain bike in the extended-cab area of my truck. I posted
some photos in June 2015.
I also have an older pair of Dahon folders (Boardwalk models). The two Dahons or the larger Montague fit under the bed in our campervan. I take the Dahons when my wife goes along, and the Montague when solo.
I know this folding-bike option isn't helpful to the original poster but thought it might be food for thought for future readers of the thread looking for ideas.
On the upside, the bike is out of the weather and dust but the downsides are:
(1) I leave the mountain bike in the Hawk all the time and its exposed to fairly high temperatures when the truck is parked in the sun in hot weather.
(2) It takes a few minutes to unpack and set up the bike, then repack it for departure from our campsite. Its less convenient than just taking the bike off a rack and jumping on for a run to the iron ranger or something quick.
As to the store-in-the aisle idea in post 1, I know that wouldn't work for me. I move daily and don't ride the bike often so would quickly regret having a bike in the aisle. I occasionally want to take a quick nap at a trailhead, check the battery, retrieve some piece of gear, etc. And in general I find bikes clumsy to move by hand with pedals ready to snag and a greasy chain ready to make a mark.