Disco 2 Gutter Mount Antenna

For those of you who might have fitted a gutter mount on your D2, did you cut the plastic cover on the gutter?

I'm getting a poor SWR reading and I'm wondering if cutting the plastic might improve it. Obviously I don't want to start cutting stuff if it's not going to make any difference.

Here’s a good read.
https://www.thunderpole.co.uk/cb-radio-guide-groundplane.html

Just been out to an open area to readjust the antenna to try and improve the SWR figure and although I've managed to get it down from 2.4 to about 2.1, I'm sure there's improvement to be had.
What I have noticed is that the inside of the rain gutter seems to have a rubberised coating on it, so the grub screws are just going in to that rather than metal.
I connected the mount itself to an exposed screw on the back door just as a test and the SWR went down to 1.4, so clearly the mount itself isn't making decent contact with metal.
I'll see how deep the rubber is on the inside of the gutter and whether I can get down to metal.

Once you have swr down get a big burner.
You can chat to more distant weirdoes

There are enough weirdos locally