You can't silicone acrylic to glass & get a strong bond.
What you are thinking of is good .... but you need to use glass instead. This is called a eurobrace. Basically you get 4 pieces of glass 2-3" wide & silicone that to the inside of the tank at the top like your drawing. <If you have an acrylic tank, a solid acrylic piece with a hole cut in the middle like yours is commonly used for bracing ..... Using 4 seperate pieces of glass (for a glass tank) is not as strong, but for a 36 gal
, it should be good enough.>
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.