After ripping the old plasterboard down in the bathroom, I have noticed quite a couple of the 2x2 timber batons are water damaged and starting to crack.

I have added several reinforcing bits of 2x2 (sawn treated rough timber) and this has strengthed it up.

I am screwing 12mm hardibacker onto the frame with aquapanel screws, and between the wood and the hardibacker is silver backed insulation (thin type) that I hope will help with moisture and heat retention.

My question is, should I treat the new unfinished timber with a sealer as its prone to moisture damage, or will the hardibacker, siliver insulation, and sealed travertine stone keep the moisture away?

better safe than sorry,if you can do anything to prevent water damage and it's easier to do at the time,you would be as well doing it!

A good case for tanking

No point in tanking hardibackers though? I was more worried about the moisture!