The foam didn't bend uniformly with heat the way I did it. Had to do bits at a time, working fore and aft along the sheet.

Could only heat about a foot at a time with a standard heat gun, then only bend that foot of material. Then move along the sheet and heat and bend the next foot. Sometimes you'd have to go back and take out some unfairness.

It was a time consuming process but worth doing properly to obtain a better finish at the end.

What is the kelsal method? What do you mean by vertical joins.