Aircon retrofit

I’ve got a 15 plate Transit Custom, that doesn’t have aircon.
This UK heatwave and a 7 hour drive in traffic has me wondering…
Can you retrofit some form of aircon unit to the van?
Like something on the roof?

It’s got a leisure battery I would probably run it off as it’s occasionally used as a site vehicle.

Anyone done this and can provide pointers?

Cheers!