When my parents had a van the layout was such at the rear was a single and a half bed with a bunk above.
We used to leave the bed as a single and the bikes just fit in the gap between walking in the door and on the right as you walked in. We used LOTS of insulation foam piping to cover the frame / pedals etc.
Our layout is completly different and too be honest would not work even if I did want them in the van....
BMW 520 M-Sport Touring, Kawasaki ZX10R KRT (AMG Eater!)
I agree, take some time and effort in arranging packaging and put em in the Van.
Put all bikes in one by one then bungee strap them together in three places so they are all as one so to speak.
Then cover the whole 'package' with Super Kingsize Duvet or similar (Buy one if ya have to) this will protect the Van interior, keep your centre of gravity low, keep your fuel cosumption as it is rather than wreck it by chucking then on the roof, oh and less chance of them getting robbed at a service station!