As for getting AC in the bed of the truck, I don't know. Even with a sliding rear window & somehow rigging up a little fan, I doubt it would get cool enough in the bed. A cap with sliding windows & pet screens installed would give fresh air & ventilation from the outside while driving. You would also want to consider a ramp for Rosie to get in & out of the bed of the truck. With her size, that's a big leap for her joints.

Have you considered a Suburban as a tow vehicle?

My parents did a truck cap and slider window for us kids.  It worked for Heat and air.  There was an inflatable thing that went in the opening.  I don't remember getting really hot or cold with that system and we had relatives 4 hours away that we went to see at all times of the year.

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Butch/Jenn: I think I'd go the Suburban route too.

I don't think that truck had AC, my dear sister. But, at the time, neither did the house. We were just used to the heat better. Truck cap had windows too, so I think parents just opened the front windows and the air flowed through.

[quote author=thingette 1s sister link=topic=3687.msg36130#msg36130 date=1501526557]
My parents did a truck cap and slider window for us kids.  It worked for Heat and air.  There was an inflatable thing that went in the opening.  I don't remember getting really hot or cold with that system and we had relatives 4 hours away that we went to see at all times of the year.

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Here is a pic of the cap boot I remember my dad's friend having on his truck.  it was somehow "glued" to the cab of the truck.

[IMG]http://i1357.photobucket.com/albums/q752/CamperDude/cap%20boot%202_zpslhukahjd.jpg[/img]

[IMG]http://i1357.photobucket.com/albums/q752/CamperDude/cap%20boot_zpsqpjuu2p3.jpg[/img]

i think if you cracked a window at the back of the cab the vacuum going down the road would help bring the cooler air back. if not maybe a corner fan.  The 2 types of seals i have seen have been inflatable and foam stuck to the cap.