making roof rack feet out of diy sugru/oogoo tips or not so pure silicone

So long back I discovered oogoo, a way to make a moldable  putty that cures into a silicone rubber substance. There's an instructable here. It's fun. The simple version is you mix "100%" silicone caulk with corn starch and mold away. I recently decided to make roof rack feet for my car. Here's what I learned:

The correct type of silicone calk has a warning label indicating acetic acid is evolved when curing. If in doubt about which tube of caulk to purchase, look at the warning label. The home depot in NE DC does not carry this product. 

A ratio of 100g silicone to 10g corn starch worked best for me. I filled the cup high and lots of corn starch spilled, but everything is fine. Mix well. Less corn starch gives a longer working time, which is very helpful. 

I used an 8"x3" plate for my foot. This is way over sized and wasteful. However I feel confident it will work. 

The method for making roof rack feet is also simple. Place a thick layer of caulk corn starch mixture on aluminum plates. Place a layer of saran wrap on your car where you want each foot. Press caulk mixture onto the saran wrap using each plate. Let cure. I went nuts and put screws at the corner of each plate to get consistent thicknesses on both sides and such. You'll have to do something to make sure the feet line up with each other and such. I also drilled a few holes in the plate to improve adhesion between the silicone and the aluminum.