Converting surface bodies into solids

Hi guys,

I've been trying to model a blended wing body using surfacing tools but after I have mirrored one side, I am failing to convert the whole model into a solid.

Would greatly appreciate it if someone could take a look and tell me why I am unable to form solids. I have tried to thicken the surface bodies which have failed and surface knit just connects the two surfaces but doesn't give me the option of making it into a solid.

Cheers,

Andy.

SolidworksSurfacing