Looking though the manual nothing is really specified about PSU installation. Of course it's not rocket science but for me it would have been necessary to have removed the screw(s) holding down the sliding PSU cover. Looking back maybe I should have noticed something off with my DG-87 as the rear door doesn't close with the smoothest operation. It's almost if something is off by a few mm somewhere causing the door to require a bit of extra force to latch.
 
When I removed the P2 1200 from my case there was a massive scratch happening on removal. I know the first thought is going to be "Why did you force it?" and the answer is simply there didn't feel like there was any additional resistance when pushing the PSU into place or when sliding it back out. I want to tackle this issue now in the unlikely event that the PSU has a failure at some point and my RMA gets rejected for cosmetic damage that was caused from another EVGA product. Especially when right now the DG-87 is still unmodified and in warranty where as in a week or two it's likely I'll have voided it's warranty by drilling out the drive cage mounts in the bottom of the case. I'm not thrilled this happened but eh, it's not really worth the hassle of complaining unless this will cause an issue with future warranty support for my PSU, especially since the warranty sticker took a hit from the opposite screw. Here's some pics of the damage

Screw that did the most damage - Should have removed both prior to PSU install and will do so moving foward
Inside view of the screw - difficult to get a clear shot of it.
Full Scratch
Damage to Warranty Sticker
 
 

You have little to worry about from cosmetic damage to the outside of the PSU voiding the warranty. 

Hoggle
You have little to worry about from cosmetic damage to the outside of the PSU voiding the warranty. 

That's what I would think but looking at the post Sajin linked gives me plenty of reason to worry. I sent ChrisB and email asking him to read this thread, hopefully he'll chime in.