Hello kr3t3n,
No your not irritating me at all, that's what forums are for, asking questions and sharing what you know. I can't always reply right away as I am quite busy these days. Sometimes I may even forget to get back to it when I have more time, but I enjoy trying to help people.
I'm not sure I understand what you mean by "using plastic grill (for weight support) under foam for growbed media?" Are you referring to same
aeroponic system your planing for potatoes, or another type of system and or plants? Anything that comes in contact with the water/
nutrients should be some type of plastic. If it doesn't come in contact with the water/nutrients, then you can use just about any material to support the system with.