I have used this one by Abt. 502 and was really happy with it:
http://abteilung502.com/product/liquid-mask/But for painting decks, myself I prefer to hand-paint them (with the exception of carrier flight decks of course). It does take some time and work, but so does masking.
The trick for me is to use enamels, and to correct the edges with a clean brush moistened with White Spirit. This way, really sharp and precise results can be obtained. Masking and airbrushing is rarely equally precise (espacially for small areas and difficult shapes) and usually needs retouching by brush.
Handpainting does usually require more than one coat of paint, adding to the workload, but the second layer goes on much faster than the first layer since the edges have already been defined.
Cheers,
Marijn