Depends how big the van is but I basically have a site safe in the van.
That goes behind the bulkhead in my long wheelbase Toyota Hiace.
Its one of
THESE and could almost have been made for Festool T loc boxes.
I can fit three lengthways, two widthways and it obviously depends on the heights how many high inside that box.
There's just enough extra space so I can move them so they slot into the grooves on the ones below.
I know you said "Without a jobbox" but I don't do trust when it comes to leaving my tools overnight in the van and as far as I'm concerned I'm making it as hard as I can whilst still being OK for my own use. Plus that box holds so much its quite a surprise to empty it all out to a massive heap beside it. Would take up a LOT of space in the van otherwise.