It's got to be smaller than a Ford Transit; that's for sure. Toyota
Lite-Ace would be nice but I guess they are too short to fit 8' x 4'
sheets in...

I've got a Fiat Ducato, which you'd probably find too big. The sheets just
fit. I'm not sure you'll find a smaller van that will take them. However,
when shifting 8x4 sheets, I almost always put them on the roof with roof
bars, or occassionally put them in the trailer. These methods would work on
almost any van.

BTW, I love driving the van. Much more satisfying than the car. You get
better visibility over hedges and oncoming cars turning right at the lights
and it has no larger footprint than a Lexus.

Christian.