I have my van setup loosely in a RB50 configuration. Here are some pics:
The Truck Vault drawer is something someone gave to me for free (seen inside the back doors). It happened to fit so I used it. As time has worn on, I would say its utility is 50/50. I use my van to haul home improvement materials and while I could lay the couch down and stack items on top, having material on the floor would be better. I've had several occasions now where I could not take my son with me since he is in a car seat (sofa bed would need to be in the "sofa" configuration). So I'm considering removing the Truck Vault and building a frame to support the cushions to the bed with open storage in the short term.
For the long term, I would consider a custom drawer design where there is 3 drawers with the center drawer being longer and easily removed, so if needed to run to the lumber yard, I could slide a few 2x4s through and under the couch.
But I'm open to other ideas so I am hoping others with similar homebuilds could post what they did with the interior back ends to their vans. I'm looking through build threads but if you have a setup that you are particularly happy with, I would love to see a pic.
Thanks!