Wisconsin Slippers

I made these slippers for my father-in-law this Christmas. I loved the pattern and they knitted up quite quickly, however I was disappointed with the felting. After moving to our Minneapolis house we now have a front loading washing machine. It works fine for felting small projects, but these took me over 5 hours to felt - and the left slipper is still a little wonky ! If anyone has any tips on felting with a front-loader, please comment.
Given that the temperature has been below -15 and my house slippers have suddenly disappeared I may be making a pair for myself this weekend.