Our recommendation: Treat your new boat cover or tent straight away with a good impregnating agent, such as Sprayhood & Tent Protector.
Why wait until your boat cover is leaking or soiled? Why wait until there is mould or green residue on the cloth? By impregnating your boat cover straight away, it minimises the adhesion of dirt and mould to your boat cover.
If you ensure the cloth is well impregnated all year round, it can be kept clean perfectly well with just water.