You seem to be missing what trials is, and what the tyres are really designed for. Trials as most people think of it comes from competitions. And you know, when it's wet in a comp, they don't cancel it. Trials tyres, and tyres that people use for trials (Maxxis Slow Reezays etc) are designed to be used in all conditions, not just the dry. So man up and just ride! Riding in the wet will make you a better, smoother rider anyway as you have to think more about where you're going to get grip and how to stop things going wrong.