El Beast - Initial design phase, comments and critique welcomed!

[Voicecoil]

+1 - you just beat me to it Jarjar as I was calculating!
I've just done the sums on a piece of 25 x 200 plate and it's something like 17x weaker torsionally than a piece of the 200x100x5 box I'm planning on using for mine: adding the bit of extrusion on the back will help depending on how comprehensively they're bolted together, but it's unlikely to achieve the same rigidity as a decent box section. OK 100mm deep might be a bit much, but there's a 200 x 80 x 6 that's nearly as stiff. And with a box you could maybe run the returns of the slot covering strips back down inside it - at least that's what I'm planning .