Neal / Jazz - thanks for the feedback.

I'll look at thickening things up, it does add up quite a bit - going from 50x50x4 to 50x50x5 to 60x60x5 each jump adds about £100 but I only want to build it once so want it to be right.

Jazz - I was only thinking of sand filling the static parts, I wasn't intending to fill the gantry - I'd be much happier not to have to do this. The gantry will be the same 160x80 ali extrusion whichever way I go with the frame.

Is the 50N loading a fair number?

Cheers!