The Kawasaki tech note describes a 3" port to access the oil filter, but having a hole that size means you need really tiny fingers to replace the filter.
I decided to install a larger screw fit marine port (hole is 6" but the actual port is 8".
The round access port costs $10 CAN.
A summary of the steps:
Remove the rear seat, loosen the left side panel (next to the rear seat), remove the battery box cover.
Unscrew two pan head screws on the front of the large plastic panel, remove any plastic rivets and finally remove the large plastic panel below the rear seat. Peel the sound deadening material off of the panel, keep it for later.
Image 1 - the panel after the hole is cut - the cutter that I used is a Milwaukee drywall bit, it does cut plastic, be gentle
The bit costs about $38 CAN.
Image 2 - after cutting the hole, reinstall the sound deadening material. Keep the circular piece that you cut out, you will use it later - see image 3.
The large panel has curves, the panel is certainly not flat, so gentle use of a heat gun will help flatten the panel. I added extra aluminium rivets to hold the panel flat to the port.
Image 4 - The port installed in the panel.
Reassemble the panel and rear seat.
Image 5 - there is plenty of space to work on the filter. (picture from floor level).
Image 6 - The aluminium panel is a heat shield, I did not need to cut it, I suggest you don't, things get hot in there.
So now I can get to the oil filter in less than a minute. Total cost was $48 CAN and about three hours of messing around.