The trouble with the site above and ones like it is the SL2 really needs a bath when you get back and the holdall ends up really dusty or muddy depending on the weather. I would like a rigid bag with wheels and a stand so you could pull it to the next section of building with you. I think a trolly would be a bit big in the van. Maybe having the wheels on one side and a fold open stand on the other, then It could be moved with the stand opened or closed with one hand.
The picture of Baudoin's solution gives me an idea. How about a half height holder that has individual compartments for each section. This could clip onto a golf type trolley as above or be lifted off and fitted onto the side of the van.
one that would sling around your side so you could remove sections or put them back in while its on you would be good.