What's the difference between 'the rules' and 'decisions' then? I've got a copy of the current rules and I've just googled decisions and they appear to be available in a separate volume. Could someone explain please? Should I have both books?
And what difference does it make whether you put a towel down or put waterproof trousers on? In the OP's scenario, either way you've got one knee on the deck so you're still building a stance whichever way you do it.
You are allowed to wear trousers (waterproof or not) when playing golf, so don't kneel on a towel!