If you get concerned about exposing the filter directly to the elements, why not try a rain sock ?
This sort of thing :
https://www.ebay.co.uk/itm/Pre-Filter-Rain-Sock-for-Stealth-Air-Cleaner-Kit-S-S-Cycle-170-0193/184217887475?epid=202987013&hash=item2ae43de2f3:g:SKgAAOSweZ9ec9Ns
I got mine from Matts Machine Shop , cheaper as well from what I remember.
I have one fitted for many years with my Morgan Stage 2 filter where the filter element is completely exposed ( and been caught in torrential rain a number of times ) with no issues.
