You could remove a couple of boards and run a fan underfloor to speed drying .
Any white sanitary sealant
So you are never going to clean it ?
Your lining is too narrow, you need 15mm either side, 12mm for plasterboard the rest for skim.
You never paint to match the wall. It’s white sealant so matches the panel.
Pump may arm may be obstructed, easy to miss small items , once checked mine three time before I found a needle jamming pump.
Washing machine needs a minimum load just as well as having maximum load.
Multi tool will cut quickly and in confined space, cut along front edge under plinths which will hide cut.
Silicon sealant , very much doubt you could guarantee no water hitting it, one slip in the bath and it’s over the ends.
Lay and sand .
He doesn’t have rising damp, no one does.
Is it a single storey ?
You will need to extend the 2x2 frame all round to hold clips.
Don’t attach the skirting to panel , fix it to base timber then offer up board and clip it in place using some keku panel clips .
Non invasive means they did not drill the wall and take a sample, which is the only way to establish damp.
Damp surveys are notoriously unreliable, how was it established you have damp walls? Who did the survey.
Use black flue
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