I hope the Sierra fit for you. I was looking at the WH R/C retracts and besides the $500 price tag they look to be top mount also. I don't know if adding a couple pieces of plywood on edgewise would be that big of a deal to make the top mounts work such as in "pattnuts" case. However we will be anxious to hear how the Sierra's do. I have been busy and the weather has been nothing but wind and rain so my Corsair has been grounded.