Sealing bulkhead panels for shower

[Strettonman]

I’ve just built the walls for my barhroom and plan to use wetwall panels for the shower cubicle. 
what should I treat the inside walls with prior to sticking on the acrylic panels ? 
I was contemplating getting a big Tin of marine varnish but will this impact on the effectiveness of the panel adhesive ? 
any ideas or advice ? 
 

cheers

[system 4-50]

I used nothing, call again in another 10 years to discover the result!

I took extra care to prevent capillary action in the floor-level joints in the belief that water does not always travel downwards.

[Kendorr]

I used this

https://www.toolstation.com/mapei-shower-waterproofing-kit/p71005

Only been done for 6 months though, so can't comment on the longevity of it.