Shower base side panels (Llanbister)

Two interlocking fibreglass panels for shower base, in delightful period 1980s-90s pale yellow.
Size 805mm(31.75") x 142mm(5.5") x 25mm thick.
One is symmetrical, the other is 'tenoned' at one end to fit in to the first at the corner (per photo).
I think these have never been used. Might be some alternative use?!

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