My stand tops were made from plate aluminum to save on weight. If you use steel, then you don't need to worry about the following.
But if you plan to use aluminum, heat control is absolutely crucial. Aluminum will warp when it gets hot, and TIG or MIG welding generates a lot of heat. So in order to prevent the top plate from warping, you only want to weld the support gussets and center mounting pole in spots, rather than running a continuous bead. If you weld a continuous bead, the top plate will definitely warp and it will be useless. (I ended up having to replace one of the early prototypes of these stand tops for exactly this reason.)
It helps a lot if you can have the plate firmly clamped in place before you start welding, but even so, if the temperature gets too hot you'll still warp it no matter how well it's clamped. So be careful how you have them welded. (Look at the pictures above and you can see what I mean about only welding in spots.) And don't worry about strength - even with the minimal welds shown in the picture above, these plates are strong enough to support the weight of an average adult without bending. More than enough for a laser projector or two!
Many people have reported this same problem. I agree that the DMX board is the problem. I'm planning to rip all the DMX stuff out on mine and install the Stanwax ILDA boards instead.
Adam