Sylvias, Kieth has been thinking about getting these guys for a while and has done his research. I feel like he has a good enough head on his shoulders to do fine with them and this post shows that it is not something he is rushing into.
That being said, I Think that the double door should not be spaces so that the snake can get in between the walls. I would suggest going for something only a cm or two between the inner cage and second barrier. This way it is still enough room to have a latch of some sort on the inside and a lock on the outside and prevent an adult spitter from getting into a tight spot which can be very tricky.
Another way that I have seen it done is with a larger custom made barrier that the main enclosure sits inside of- inception style. Then you could open and lock one tank from the top (or side or wherever) and then take the other out when you need to access it. The only issue with this is how to remove the snakes enclosure safely and easily. This works best with smaller tanks but it may give you an idea.
I am not a huge fan of double doors but if I am correct, your country requires them. Ask your officials if you can have the snakes in a dedicated, sealed room. That way you could add weather stripping to the door, screening to any vents and locks to the windows and door and vivariums and be set. I think that is the ideal set up when it comes to safety and ease.
