I use Petrowrap
to protect exterior metal hydraulic fittings, but I found a new use. My Wema black water gauge has stopped working, and in inspecting the leads to the sensor I noted that the sanitary line from the black water tank was pretty aromatic. Wrapping it in Petrowrap eliminated all odor, and I would think that given the composition of the wrap, odors could not penetrate, now or ever. Worth a try, anyway, and very easy to apply.
I have fittings that have been wrapped in Petrowrap outside for 5 years, and the wrap is as fresh now as it was when first applied.