The fire burning at the Vale Business Park in Llandow is now out.
It began on November 26. A spokesperson for South Wales Fire & Rescue Service says efforts to tackle the blaze were hampered by the construction of the building - a former aircraft hangar built to withstand bombardment.
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The heaviest bursts are expected in the south and east, with some western areas either remaining dry or becoming dry by dawn.
Many places will start dry, but rain in the southeast will spread to most for a time overnight.
The family of Isaac Nash who went missing after being swept out to sea last summer have presented a cheque for £10,000 to the RNLI.