bolt-on plates for holes in inner door shell?

Hey guys, I saw this pic in one of the threads the other day... it looks to me like he has some prefab'd metal or abs plates bolted into the holes in his door shell. I'm working on sound system & noise deadening upgrades and would LOVE to get my hands on something like this. Anyone know where I could find some?

PS - I realize most folks just dynamat over the holes... I just never liked that much.

 

That would be interesting if pre-made panels exist, depending on the price. You can always make your own with some kind of plastic sheet material and rivnuts.