+xAdditional stiffening would help but care needs to be taken not to make it worse. You can wrap it in release film or similar and use an electric blanket to get a mild post cure which should help. The release film will stop the blanket sticking.
Thanks for the reply Warren. Does the additional stiffening potentially make it worse due to stress concentrations? I have noticed that the flanges running down each half are not parallel (due to the slight ovalisation of the mould?). In order to make the flanges meet each other and close the split, the flange bolts have to pull the flanges back to parallel.