Guterman is not a strength. Go to DIYGEAR
and see that Scott carries 2 (of dozens) of Gutterman's threads, in a total of 4 different thread weights, 2 of the light ones pretty similar.
Lock-stitches are rated at 1.7 x the thread strength. Say the strength of your polyester thread will be 4 - 8 lb, (Tex 35 - Tex 75), you sew channels @ 12 per inch, 2 rows, across a (narrow) 48".
Yes that 1.7 x 4 x 12 x 48 x 2 is a large number, about 10,000.
Even after some degradation from UV, you have a very large operating margin of safety.