That pipe insulation seems more of a headache than anything to be honest. It's not the type of foam I was referring to either. You know the grey foam that is on the walls in sound studios or movie theaters? That is the foam I'm speaking of. It's called acoustical foam. Google for either a fabric store or foam shop near your home. Otherwise yeah just order one online. Look online at photos of the platforms to get an idea.
All they are is a piece of 1/2" MDF with cloth wrapped & glued around it. Then a couple strips (2"x4"x length) are glued to bottom sides with the same foam, but convoluted, glued between the runners. That's it!!
If your getting a new sub, add the cost of the platform into the total. Using sub-par materials will give you less that optimal results!