I have an aged Smart Alec with Steel exterior (Solar interior!), and lately I've been noticing that the top of the Steel portion is looking pretty grungy. I think I'm clear on how to wash it (use a mild dish soap, let it soak for a while, use a soft toothbrush to scrub anything that needs scrubbing), and when re-waterproofing with Nikwax I know to apply it while the bag is still wet, thanks to other Forum members' experiences.
However, I haven't noticed anyone talking about what parts of the bag they're applying the waterproofing to. Should I apply Nikwax to the lining, too? Or just to the exterior?