Those coroline sheets are ideal and will last a long long time however they are not cheap. If you need a quick and easy fix go to the Screwfix website and search for the "No Nonsense Water Repellent" sealant. £15 for 5 litres and you can coat anything, wood, brick, felt, cement etc etc. It is amazing stuff and you just brush it on in minutes, no fuss. As a quick fix should sort your problem for a year plus then you can just re-coat as/when the problem returns.