Nice, if pricey....I suggest before you invest in those, figure out what you want to store in the basement, and then weigh the stuff. You might be surprised just HOW MUCH weight you could put in there!
A simpler alternative is to use the ordinary (as equipped, or installed) cargo areas....and use simple but very sturdy drawers with ordinary heavy-duty casters attached to them...either affixed to the sides or bottoms of the boxes.
Or, ANOTHER alternative is a set of rollers like they use for moving boxes off of trucks...fixed in the bottom of the storage area they will permit simple boxes of almost any size to be used for storage.
The rollers are easy to remove from the frames, just push in one end of the roller axle (you'll see which) and it lifts out.
This can be adapted to any system you choose to use.
I would have the basement door fold DOWN to act as a platform for the drawer to roll out on. Support the basement door with cables or such.
You can also find good cheap rollers at equipment handling places, trucking firms (retired equipment etc.).
And you are not forced to use the rollers fixed in the bus...you can attach them to the bottoms of the boxes themselves instead.
Just make certain that the drawer retention pins or locks you use will not permit the drawers to slide out on hard turns! Not good to see your stuff along the side of the road!