I'm considering installing a fuel-water separator to help with the E10 fuel we have here in CA combined with my "open vent" style fuel system. Something like this:

https://www.summitracing.com/parts/prm-81794/overview/

Has anyone else experimented with this?

No but it looks like a real good idea. Twice last year I had water / fuel issues. It really sucks being stranded because of this. Looking ar Amazon, there are a lot of less expensive options

Yes use them all the time, between my diesels and my boats, all have water separators.

I would put it before the EFI pump, but it can be placed on the pressure side. It will handle 90 psi.

Mounting was my next question. So this could be mounted in the back before the injectors?

yes, lower left corner of engine bay, put a heat shield on it, for protection. And move your fuel pump forward if it is not all ready there. The drain cock on the bottom will allow you to drain the water into a tub. As it sinks in the filter. So you want a place you can get to it, and drain into a clear container.

Here's what I use between the tank and the pump inlet up front next to the fuel tank:

http://racorstore.com/racor-120r-rac-01-30...-on-w-head.html

So, it’s under the belly pan? I was concerned with that one due to what looks like a plastic bowl.

I like the idea of seeing the water. I am concerned that that one must be used in a low pressure (inlet to the pump) side. Were you able to locate this under the tank? Is the petcock accessible? I like the idea of using this on the inlet side to offer protection to the pump. One time I had water in the gas, the pump ran starved