I've decided to try my hand at the 18.5 Walrus. Got a couple questions: I have a 21' two-by-ten that I'll rip for stringers but I don't know how many strips I'll get because the lumber is old and not in great shape. Which of the stringers demand the most strength? Second, does anyone know price comparisons for canvas and the alternative coverings? Third, does anyone have sources for the various possible coverings? Thanks, Tom