Hmmm...
You did a pretty good job bashing out the blisters at the axle junction, could you do the same out of a piece of aluminium? Haven't used plastic yet on the car and I am loathe to do so at this late stage.
The blister is all very well and good as a shape on its own but remember the junction to the bodywork needs to be smooth too (radius of 500mm?) to minimise drag. This can be bog.
I'll be there in April so let me have a look then!!!
Dik