Mounting a heavy PCB in standing position
The solution for this would be some rigid support rails that run up the side of the board, and ideally anchor it top and bottom to prevent how much it can flex, The top of the board is where most of the weight is, so I would strongly recommend you look for any way to make sure its secured some way at the top. 

if you cannot, you will need to make up with thicker support rails, usually rectangular profile screwed to the board at the corners at minimum, more usually top bottom and center

In addition to this glues similar to the craft hot glue are used to secure each capacitor to its neighbors (a small amount in the gaps) this way they cannot work harden off the PCB