Hi Trev,
Wow that looks great mate
I think my soundproofing was sticky backed, but if not I would use something like CT1 to fix it. Or simply ask the supplier for their recommendation. I could ask Pete in Quay West chandlers if you want.
On Alfresco the edges and joins were sealed with tape bought from the same supplier as the sound proofing sheets.
I remember that this quite expensive though.
Ref the chequer plate, I left mine bare and it is still in good nick after 18years, it has dulled quite a bit now though.
Gary Austin treated his, when he built Prodigy and it stayed looking like new.