I have been using perspex plastic on my watercolour sketching board. I wet the back of the paper then tape it down. After that I wet the front of the paper and let it settle. This isn’t actually my new technique. I am placing a damp cotton sheet between the paper and the perspex before I tape it down. This gives me lots of time to work on my clouds but I have to get used to it. My watercolours are a little pale at the moment but I’m working on it. Practice, practice.