I found that just relying on the clamps on the top pulley mounts to keep my belts tight was not all that great. For starers you need four hands to apply tension and tighten the nuts and bolts and its hard to fine tune. Also these are smooth rods so overtime the top could slip down.
Since 3/8" threaded rods are real cheap, I added two at the back corners and one on each side towards the front. Now I can just turn a nut and get the belts as tight as I want.
As this was not in my initial design I had to as small metal plates that I just had lying around to get the rods at the front clear of the movement. If I was doing this from scratch I would change the shape of the top and bottom pieces so the angled out a little towards the front to cater for the rods.
These rods could also be used to attach angled brackets if I want to add more rigidity to the frame.
My next mod will be the relocation of the Extruder. I worked out by suspending it below the top plate about 19cm below the top. It will sit right above the head just clear of the home position and shorten the Bowden tube by almost 50%. Is an easy mod I will try it during the week. I am hoping that shortening the Bowden will improve its response after a retract.