Corrosive/ Acid cabinet gets wet from time to time I have a metallic acid cabinet in a chemistry-based lab which I use store hydrochloric acid, sulfuric acid and ammonia. I also store nitric acid together inside but they are physically separated from the rest by an additional PP plastic case inserted into the acid cabinet. 

The issue is that from time to time, I realized that the doors and secondary trays in my acid cabinet will get wet, especially the area near the sulfuric acid, and white powdery crystals sometimes form on the walls of my HCl bottles. I have ensured that I tightly sealed each of the bottles. Can anyone help me out? Is this dangerous? I'm trying to seek a solution before anything serious that might happen. 

Also I have a few bottles of unopened, still sealed sulfuric acid which have turned black but the acid is still clear and usable when poured out, is it still alright to use for experiments? Will the results be affected?
The white powdery crystals are probably $\ce{NH4Cl}$, that is formed thanks to leakage form amonia. You can try to measure the pH of the wet layer, should be acidic because of the leakgae from other acids bottles that condensate on inner walls. Most experiment results should be ok, but if you are working in an analytical lab, the results can be shifted.