Rails for 2 Post Racks

[Optimus Prime]

I installed a 2 post wall rack...now I I want to install rails for a 4U case and a shelf. Without posts in the back, do I need to bolt the back of the rails to the plywood, or can I go without and rely on the front rail bolts to hold the rails?

Thanks for your feedback.

If anyone in DFW has a short depth 4 post wall mountable rack they want to let go for a deal, let me know...

 

[Holbs]

trying to picture 2 post wall rack = wall hanging network cabinet (open or close frame)?
As for trying to decide the need for rear rails in a cabinet, you have to ask how much weight will be there. Some components will allow you to move the front brackets back a couple inches to help distribute the weight better upon the front 2 rails.
I have a wall hanging network cabinet and everything is only attached to the front rails (patch panel, 48 port switch, shelf holding cable modem, router, NAS, Blue Iris PC), except the 19" rail mounted battery backup which just sits on bottom due to the weight. I could get a 4 post shelf (attach to 2 front / 2 back rails) but eh...it's ok sitting there.

 

[Optimus Prime]

It is an open rack.

 

[Holbs]

you could ask your local cable installers if they have an older 4 post rack laying around. We have 10-12 collecting dust that were acquired when folks move out. Just taking up space.