As long as your gravity is going down you can feel certain that your fermentation is still continuing.
The specific gravity is in fact the only way to know, so you're monitoring your fermentation the right way.
You should be fine with your nylon
According to this boiling point explanation where the boiling point is raised by 2.8 C, you'd need a SG of over 1.350 (round number, but I think the point is clear) to even raise the boiling point by 3 degree C!
I personally think the physics in the linked example is hard to understand, but suffice to say that if you keep ...