I think you have the information you need I am just going to point out two things. The heat packs ment for hand get very hot so a some method of separtating them from direct contact with the snake bag is important. (tape to tape it to inside the lid with a few bits of paper towel). The second thing is about air holes, I don't know where you are but holes during the move from out side to car and car to inside might not be a good idea. The cold air can shock the lungs and open the door for RI. I'd say no hole at all if it is cold where you are (-4ºC today where I am) once the car is warm you can pop the lid and open it up a crack for a bit. in a bag the snake can't go far. Same for going inside button that up so the cold air isn't hitting the snake at all.