Back in Clive Trickey's days we used to use an MGB centre box as a back box. It was oval but very shallow and didn't get ripped off so easily as the standard cooper box.
Thanks guys for your input. Maniflow freeflow seems the way to go agreed.
I'd still appreciate some viewpoints on the sprite back box
Do you mean an Austin-Healey Sprite Mk I? The "Frogeye"?
Yes the frogeye. It's a bit old school but I noticed Clive Trickey recommended this.
Will bear that in mind next time around. Did it sound fruity?