Gaffa tape, roll the cloth and then bitumen flashing tape over the fold. By the end they had three crack teams of seamers. There was suprisingly almost no leakage during the night, we had allowed for a fire hydrant to flow in all night but it was left off!
They used empty vodka bottles filled with boiling water to make the tape more pliable when it got cold (I used to put it in an oven, but forgot to tell them). With that quantity of seams I think the vodka was a mandatory accessory amyway....
