At first you have to know that there is actually difference between mold and mildew. Oh my god in my mother tongue they have exactly the same name, but let's find out what is mold and what is mildew.
Both of them are types of fungi. Typically, mold is black or green or blue or yellow, and mildew is always grey or white, sometimes brown. Mold tends to grows on food, whereas mildew is an issue on damp surfaces, like walls or fabrics. Mold grows in the form of multicellular filaments or hyphae, it is fuzzy, while mildew has flat growth.
Now you has to be sure that on your old PVC cover that thing is mildew. We have bad news, mildew can cause health problems like respiratory damages or chronic headache. There are commercial sprays what kill it, you can use the mixture of bleach and water (think green please, take care of mother nature!), sometimes strong vinegar can help.
Some good materials for maritime goals like Sunbrella have anti-mildew coating. If you are looking for a winter coat for your boat, or you will leave it for weeks in the boatpark, we recommend you to use a cover made from these materials. But if you use your boat almost everyday the best choice for you is UV Covers. UV Covers will be never covered by mildew.
You can apply very fast. It's breathable, so the boat will be dry under it very quickly. It's not waterproof, but it's UV proof. Don't forget, that the biggest enemy is the sun for your boat, not the water.
If you think different, go and choose an other, less wet sport. :)