Ok,I've got 3 sheets of 500x500x24mm how about if I was to weld it together and get some 1 or 2mm plate aluminium off ebay(quite cheap and I don't need a lot) and use 1/2" M6 seltappers to screw the plate to the sides of the gantry,that should strengthen it a bit.

Will use either Superglue orAraldite or even Dichloromethane ifI can get my hands on it?