Why did you epoxy the whole base.? You will need a base board or fixture plate and that will need to be surfaced so it seems like a lot of wasted epoxy to me.?

To me sitting the rails on profile to raise the gantry defeats the point of the concrete base as it introduces a weak point which could have been avoided by creating raised sides by shuttering up and filling with concrete, then epoxying just the raised surface. You could have then fit tooling plate to the surface for the rails to fasten too, it could also have been used to fine tune out any errors.

But I suppose the beauty of concrete is that you could still do something like this if you wanted without too much hassle.