I have Tone's door popper installed in my VX and his kit came with a rubber bumper, or sorts, with a contained spring so it wouldn't mess up the finish on the door. I don't have the spring installed in the VX, but I do still have it at home if you'd like me to take a picture of it so you can get an idea for your kit.
The raw spring would scare me a bit as I would be afraid that it would scratch the paint or plastic (depending on what it is pushing on). That's just my two cents.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless