Firstly, consider how long the laminate will last because over time it will show the signs of water damage, no matter how much assurance the company give.
Secondly, if you go ahead with installation the amount of expansion will not be excessive unless your bathroom is extremely big. I would recommend fitting the loo and basin on top of the laminate and not being too concern about the expansion. What you must remember is to keep the expansion around the edges. I would only install the laminate to the feet on the bath, just enough to be covered by the bath panel.
Personnally I wouldn't install laminate in the bathroom but install tiles as they will wear better than the laminate.
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