I'm new to the string-your-own world, but enjoying it... I'm about to cut some string to do a 1-piece job on my Aerogel 200 (95 sq in., 18x20). is 38' 6" going to leave me short? or should i play it a little safer and cut 39ft or even 40ft? --also, I think I will use 10'6" for 1/2 the Main. will it work?