Do such designs ever occur on north facing rock where the sun never shines?
Not very often so far as I've been able to ascertain, which is one of the things that got me wondering (though few such details are usually clear and it's horribly hard to pontificate without "being there".).

The second question is to ask if the same sort of design is ever found within structures - again where the sun cannot reach.

Yes, lots. BUT I have an idea that those sometimes have upwards pointing tails, suggesting that they're derivative, purely symbolic ones???

If there's any merit in the idea of a specific practical origin for the design it has to be taken on board that practical and symbolic may both be present. You could say that's just a cop out to explain contrary evidence but on the other hand they do reek of symbolism as well as practicality. They're typically human markings!