thanks for the info.

I'm probably over thinking this I'll build the printer see if I have any problems first with the metal print bed, just checked it would actually be cheaper just to scratch the bed if I need to than to use buildtak or kapton tape (there more expensive than the heated bed) I'm making my heated bed in a way that if it needs to be repaired or replaced then it will just unplug and I'll just plug in a new one.