I have a 2006 RC100 that I took delivery on in 12-2005. I'd like to tell you what I did to address the dust issue.
After a lot of research I decided on a MacBone Industries pressurizer. That's a fancy name for nothing more than a Jasco blower, rated at 250CFM at 2.3 PSI, coupled to a Donaldson airfilter housing. The blower is rated for a service life of 1000hrs. The unit is mounted on the cab roof in front of the AC coil under the enlarged brush guard. I don't miss the view through the roof but if I was to do it again I would mount it on a piece of lexan rather than plate steel. I found a nice AC vent out of junked car to direct the air in the cab.
Of course, as Ax Man mentioned, a lot of dust enters around the seat and controls area. I cut some pieces of dense foam, approximately 1 1/2 square, in various lengths, to fit in these areas. It takes about two minutes to set these pieces back into place once the cab is reset back down on the frame. I also use a portion of a quality household AC filter to replace what positrac uses under the seat. In addition to weather stripping the cab to frame surfaces I used silicon caulk to seal up all the little joints under the seat and in the door corners. The openings where the hydraulic motor supply lines that pass through the chase have been reduced with conveyer belt material All this has worked together to eliminate any noticable dust infiltration in the cab.
I am also in the FL panhandle. I was concerned that I would not feel the AC when the unit was running. Well I can honestly say that I don't run the AC near as often with the outside air blowing in and the cab stays comfortable even on the hotest days. I have had this unit in place now since April 2008 and its working very well.
