What are you using for the filler material?
I use PC7 2 part epoxy. It's about the consistency of roof mastic and just as sticky. This is my second steering wheel out of a 1 pound kit. This has been in the shop about 3 years and is fine. A 1 pound kit is about $22 but a 4 pound kit is only $47. I called the manufacturer and ask if I should use a plastic adhesion promoter and we determined to let the epoxy chemistry work on it's own. This stuff really sticks. I put a marble sized ball on a polished pyrex 3/16" rod and put it in my sanding water to cure just for a test. I had to cut it off piece by piece it stuck so well. there was a little milky film on the outside but otherwise fine. It sands at about the rate of body filler.
