I had the same problem, no room to put the actuator under the seat, so I mounted it here :-

Then I fashioned a cover out of plastic gutter downpipe, with a cap at the upper end:-

It's a tight fit, but has worked flawlessly for over 8 years in all weathers.
For the vacuum chamber, I fashioned this out of 1-1/4" plastic waste pipe:-

and fixed underneath the swingarm.