I've driven with many a hedgehog in the vehicle with us. Where the carrier is located depends on the direction we are going and the time of day. The carrier goes on the side of the van the sun isn't shining on. Sunshades work great but so does a small blanket, towel or baby receiving blanket hung in the window. Open the window, put the edge of the blanket over top, then close the window. Works great. Since you don't want to block your windows or use the back seat, that idea won't work. Using a window shade or a piece of cardboard propped up against the carrier to shade it will work or a child's umbrella will also work. Anything to keep direct sun off the carrier but still allow air movement around it. The dollar stores sell these tinfoil covered foam sunshades and they work great for not only keeping sun off carriers, but wrap the carrier, foil side in with it and it will hold heat in. They are cheap $1, cut to fit if need be.
Cars are a little more of a challenge. We have a van with rear a/c and heat so we can sit up front in a temperature we are comfortable at, and hedgies can sit at the back with a temperature they like. We can also block the rear windows so no worry about sun on the carriers. I take one of the remote thermometers so I always know what the temperature is back where they are. Works great. :lol:
Cars are a little more of a challenge. We have a van with rear a/c and heat so we can sit up front in a temperature we are comfortable at, and hedgies can sit at the back with a temperature they like. We can also block the rear windows so no worry about sun on the carriers. I take one of the remote thermometers so I always know what the temperature is back where they are. Works great. :lol: