Ok so I started looking into positioning a bottle in the window drain area and found the MX5 relocation washer bottle kit pictured. Dimensions; 34cm wide and about x 9cm x 9cm. These dimensions seemed too big to fit the MB.
Universal bottles had a similar problem, all too wide to fit anywhere neatly, I thought about hiding one inside the wheel arch.
I found a motorcycle brake fluid tank off ebay ($13 delivered) and an inline washer pump ($5)
I put the tank under a strut mount bolt and cable tied the pump in place (no drilling). Yes it is very small, It holds 50ml plus however long your hose is to the pump. I timed it at 4 solid seconds of use, which should do me fine considering I haven't had one fitted previously.
If I find I want more capacity or think of a better place to put it I will. I hope this sparks some ideas for anyone else looking to add/move it.