Power Distribution P5

[Croydon Lights]

I am using a couple of MW LRS-350 to my P5 panel
Do I need to tie the DC side together between the Mean Wells or not as the panels are connected together

 

[Skymaster]

You shouldnt need to. Ground will be implicitly connected via the data cabling which is fine.
However, try and keep each chain of panels to a single PSU, as some panels (not all) connect V+ over the HUB75 interface.
eg:

If you have 16 panels in a 4x4 fashion connected to 4x Panel outputs, driven by 2x PSUs, make sure all panels each row are on the same PSU. Don't do it column based.
1-4 < 1-3 < 1-2 < 1-1
2-4 < 2-3 < 2-2 < 2-1
3-4 < 3-3 < 3-2 < 3-1
4-4 < 4-3 < 4-2 < 4-1