That thickness of glass... the might be a bigger concern of the glue giving out. That glass isn't likely going to 'bend'. Although the plastic isn't going to give structural 'strength', it would add structural integrity. The corners being the biggest issue. If the frame wasn't made with a center brace, then this would make sense where thinner glass tanks would have central braces to help stoke the overall structural integrity. The point is the glass doesn't need to be that thick assuming a sturdy support frame; so consider all those rimless tanks if you ran the math on their thickness it'd probably scale up to about your thickness (where that extra frame sturdiness is also there. If you have the frame able to slide up and off currently, you might fill it and see if its still loose. Or you could go apeshiite and extra glue the corners of the frame on and be stoked that you dont have to have that central obstruction. All opinion of course!!!