With the length being 1000mm do you run into any flex or undesirable movement? The project size that you built is about the same as what I plan on building. However I am going to make the sides a little more beefy by bolting them to 4" aluminum angle 1/4" thick. I am not sure if I am going to cut the angle into 4"-6" pieces or just leave it the length of each side. The aluminum angle isn't terribly expensive considering what the extruded aluminum costs. Here is a link to it on Amazon if...
Base Rail Support Brackets
Base Rail Support Brackets