if hes going by car id suggest a poly box with small rubs inside and run a heat mat from a 12v converter to the cigarette lighter. when the engines off to save battery power he could then switch to heat packs to keep it warm inside. Once off the ferry, switch back to the heat mats on a stat. If hes struggling to get a poly box, a normal carboard will do and line it with poly sheets.

I would say use the cars internal heating system but to be fair youve gotta drive in that heat and depedent on weather if its hot outside theres a good chance he will want the air con etc on.

 

Are kingsnakes banned in Spain? I think they might be, worth investigating.

 

To be fair unless it's freezing, which it wont be, I wouldn't be worried much. Perhaps if they're left in the car during the ferry trip then a heat pack would be beneficial, can get chilly in the holding bays.

30 hours in a suitable container in what is going to be a generally warm car on the road (even with air con).

But that's just my opinion.

I'd definitely take heat packs in case the journey is delayed. And if it's really badly delayed and there is a stop over then I expect they are taking the proper heating equipment with them anyway.

 

Three of these species would be fine, even if it got quite chilly. Even the boa will be more resilient than many people would predict.

 

Totally unrelated to the actual question, but thought this might be useful if your friend hasn't already seen it

http://www.mapausa.org/eng/nc_5.htm