I’ve thought about buying chrome 3m vinyl and doing just the roof before but my last van was white so I didn’t bother. There’s no way it wouldn’t work to some extent but I’m yet to try it.
I did fit a Fiamma roof vent to my Tranny Connect and that was good for letting hot air escape but you can’t drive with it open.
If the cab has AC you could try ducting from a vent or two into the boot area where the dogs are. Like the stuff racing car drivers dangle in front of their faces.
Actually just cut holes and fit NACA ducts in the rear panels. Full racing Berlingo.