Gidget has an older Mountainsmith pack with removable saddlebags. They don't make that design anymore but ventilation was taken into account with their current saddlebags.

http://www.rei.com/product/787812

"Mesh straddle panel and open strap design allows ventilation"


You might also call this dog pack company in Ashland, Oregon, that has been producing packs for nearly thirty years. The owners, Linda and Paul, have Samoyeds and have been pack-hiking with them for years. Perhaps they can do something custom if you don't think their packs will work. They are very nice people producing a great product.

http://wolfpacks.com/

Wolfpacks is on Facebook:

http://www.facebook.com/pages/Wolf-Packs-Gear-for-Working-Dogs/92458914506?v=wall

We are now offering our Banzai dog packs in neon pink, a color so bright it can probably be seen from the Moon. The black ballistic fabric characteristic to our Banzai is a prefect accent to the vibrant color. These packs are sure to make you and your dog smile while you are out on the trail together. We plan to continue production of this exclusive color through the end of 2010.