Would there be a way I could convert the Grainfather 70l fermenter so I could pressure ferment? A way to clamp the lid down?
I would say yes there is using the bolt holes in the leg to set up an adjustable clamp on the top. But I wouldn't bother, if you are wanting to do closed transfers get a PET fermenter as a secondary and put another brew in the stainless fermenter.
Funny I was reading through my old BYO magazines from 2011, no mention of pressure fermenting or closed transfers and yet everyone was still managing to make first class beers, barely a mention of oxidised beers. Just goes to show the influence advertising has.