1342,
I have no idea if Wilson makes a 'groundplane kit' or not. I would suspect that they are smarter than that though. Anything that connects to the vertical portion of the antenna, the 'radiating' part, is not a groundplane, can't do anything that a groundplane would be useful for. It's a 'gimick', a magical device that transfers money from your pocket to 'theirs', that's it. Don't fall for all the advertising garbage you hear about them.
They can be useful in particular cases though, but as a 'capacity hat', not a groundplane. If you have use for such a device, they should work. If not, don't be fooled into thinking they are something they just can't be. There's enough of that sort of garbage floating around now.
- 'Doc