Fitting twin horns

I 've fitted twin horns on other cars in the past by just removing the single and connecting the new hi-lo pair to the original wire. I was young then. Now I'm more cautious, whats the practical thoughts on doing this on an Octavia Mk2? If I use 2.5mm2 wire I don't envisage a problem, but if I ask questions the recommendation is to fit another relay and add a fused power wire from the battery. That makes it a tedious job. Does any of the Mk2s have twin horns, and what size wire was used?