I might look at putting a Kolpin hard case on the backside of the ladder.
Thanks for the ideas.
I considered the Kolpin and similar as well. The downside for me is that (1) it looks like a rifle and (2) it needs to be mounted with the barrel pointing down to be relatively easy to use.
My idea now is to get an peli case, rip out the interior and mount two Railblaza gun holders per rifle (one low at the stock and one high at the barrel), and put two rifles per case. Then mount the case vertically in the rear window MOLLEs. One per side. That would hold 4 rifles, which is normally enough.
Links;
Case: https://lindelarsen.se/shop/peli-hardigg-rifle-case-m16-3/
Gun hold: https://www.railblaza.com/products/gunhold/