This is just a personal preference. I find velcro often comes loose.
Plus it picks up dirt and water.
So we therefore use the body posts that are already in the kit:
First grind off the collars.
You'll need to later drill new holes to fit the battery brace.
In the front we use the std. B4 solution.
Put a nut in the hole where the posts used to sit. Fix with superglue.
Make sure it sits flat (test with screw before glueing into place).
Add approx 3mm shim on top of the nut.
Now test for fit. Adjust by adding/removing shims under the posts.
The posts should be long enough to protrude from the bodyshell.
Drill new holes, preferably in the length direction of the car.
End result. I've cut off the straight part of the body clips a bit.
Put a nut in the hole where the posts used to sit. Fix with superglue.
Make sure it sits flat (test with screw before glueing into place).
Now test for fit. Adjust by adding/removing shims under the posts.
The posts should be long enough to protrude from the bodyshell. 
End result. I've cut off the straight part of the body clips a bit.