I am using the Duraslope that you mentioned, but it doesn't have a lot of use on it yet so I can't speak to long term durability at this point.
What I can tell you is that if you plan to have any forklift (or even pallet jack) movement over the drain then the HDPE covers will not survive. I have already broken 3 of them moving a grain pallet over it. If you are super careful and only move the pallet jack wheel over the grate where it is supported by a cross member, then you'll have better luck. It's a pain to try to navigate through cramped space like that though. If you aren't driving over it then the plastic grates are fine in my opinion...
Blank Slate Brewing Company