We've been rescuing for a long time, and currently have 5 pups living with us (and 7 more in little oak boxes on the mantel).
When you think of buying for a non-profit, think of the Income Tax rite-offs!
I know that you aren't thinking of a new unit, I'm only showing you this for the purpose considering a "toy hauler". The rear of this one is a 8" X 9" foot garage, that will haul a bunch of crates. The rear door is a ramp that also will become a 6" X 7" foot fenced patio deck, which would be great for grooming, feeding, or just the fur babies getting some fresh air.
Just something to consider.
https://thormotorcoach.com/outlaw/class-c/floorplans/
Good luck!