I'm using a Factory Five inline filler with provision for an overflow tube. It's mounted at the high point of the upper radiator hose. The overflow tube is connected to a translucent plastic coolant recovery reservoir in the driver side wheel well. It's not ideal because it's a PITA to top up, but it certainly can be done. I'm thinking of putting something different in the engine compartment in the space between the radiator and engine.
The filler is kind of like this one:
The reservoir is similar to this:
