I did this mod several years ago, before I joined this forum. Since I was working on the quad this past weekend, it seemed a good time to share the upgrade.
The stock airbox was awful, and it was very difficult to get to. The entire front half of the body had to come off for access, and that means the filter will be neglected.
I used the stock boot from the original airbox, and I inserted a piece of ABS pipe and clamped it. I cut a hole in the plastic under the seat, brought the ABS through the hole and clamped a Uni pod filter onto the pipe.
I also cut up an old water jug and zip tied the plastic to the frame to act as a splash shield.
The filter has always been dry since the mod.