"Check out my weights on my build. I got the idea frim Dragons Breath and they work perfect. I used a 2" square tube (because I had it and didn't have to buy), and I then filled it with a piece of 1-3/4" round solid stock. I simply built the weights 1" wider then the doors and put the solid stock in them. Fortunately it was absolutely perfect. Now my 60# doors weigh about 3-5 lbs. And they stay up when opened. I cut a template of the radius of the tank, put it on a piece of 1/4"plate, went from 3"wide at the tank end to 1-1/2" and 24" in length. I attached them as high up on the tank as I could.
As for your racks....I used a 1" thin wall tubing covered with a3/4" shaker screen I picked up from the scrap metal yard for 60 cents a pound. They are way strong.
Your build is looking good.
I, like Dragons Breath, used toggle clamps (500# ers) I just bought 10 more of them for $4.80 each, with shipping they came to $5.68. Thetogglestore.com. lowes wanted $24.68 each special order for the same clamps.