First time building an home

[-=Mel=-]

Hi all,
So we are getting two Hermanns hatchlings. Very excited and very nervous.
So tomorrow I am building them a house for their first year. The plan is make it big enough that should they need to be split then the box they are in will be suitable for at least long enough to build each separate spaces.

So after much research, drawing up plans then scrapping them and starting all over again I think I am ready to go to the wood place tomorrow.

I am going to use a hardwood ply 18mm thickness and make a home 4ft x 2ft with a hide at one end. I am making it 14inches deep as we have large dogs and don't want their noses to frighten the smaller creatures.

So anyway long story cut short how do I seal it? I am considering using a portex paint which is super animal friendly however not that convinced it will prevent the ply from getting damaged. the ply itself is going to be screwed and glued together to prevent external leakage but how do I stop it going rotten from the inside.

As their home is going to be quite a feature in our home I don't mind splashing out on making it right.

Any ideas or suggestions?

Many thanks