Having struggled with all of the above possibilities and issues ( new Cali and old smelly, restless canine ) am currently compromising with a customised metal travelling cage that I have insulated inside . I have a waterproof cover with breathable door and blocks underneath to raise from the ground for outdoor use . Milo travels in the cage with the seat up and sleeps outside under the awning with the cover on. He seems happy and in fact tended to get too hot in the van at night and became very restless. During the day he likes to doze in/ out of the cage/kennel after his ( increasingly brief with age) assorted perambulations. We now use this as his permanent accommodation at home so he is totally accustomed to it and associates his evening retirement with a final biscuit in the cage / kennel ..... It has a wide front doorway that I leave uncovered in the warmer weather ( soon ??) for additional ventilation.
So far so good...
al, put