Sorry? Weekly bathing? Um no... That will just make your horse's coat quite dull.
Ever heard about the natural oils in your horses coat? Thats what makes their coat nice'n shiny. When you brush, you spread the oils out around the coat- but when you shampoo you wash them out. And they go bye bye. Of course just one or two baths (with shampoo) in the period of a month won't hurt. But.. If you start doing 3 full baths a month for a couple months... Say bye to a healthy coat.
Also wouldn't recommend fly sheeting them 24/7, why not put it on in the morning and off in the evening? Otherwise the poor horsies won't be able to scratch and roll (which actually helps make their coat shiny!).
And- don't take it personally, you almost sounded like a horse beauty practitioner "the soft skin needs some spf", just made me smile!
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown