I have not, but am thinking about it. I think for short trips it will be fine, 1-2 hrs, depending on temp. For longer trips would not be ok, if it's hot.
I am interested in thoughts as well. I know our dog would be much more comfortable in the TT than the truck.
I have put him in the bed when I had a cap, used a 12v fan running on him with windows open. He always did very well that way.
2015 Ram 2500 Laramie, MegaCab, 6.4 Hemi with 4.10
2015 Jayflight 28 BHBE
Equalizer 14,000 lb hitch with 12,000 lb ball and arms