Great job!
You could try to find a bottle the right diameter and cut the bottom off to fit over the Tachometer! Or make a cover with a piece of plate glass cut round and some rubber hose the correct diameter!
Such a cool / low budget build!
My bike has the tank to fairing mounts exposed too
I was thinking of putting a 90deg bend in some plastic sheeting and then trimming it to fit to the tank to give the tank some sharp angles on the front edges
I have been thinking about replacing my coolant res with a SS flask or something else re-purposed.