In my 14.44 I only had the privacy screens, handled a few good gully rakers including a hail storm and no water got in, they allow better air flow.................I very much doubt storm covers will stop mould on the bed ends, moist air will still be there either way if the sun isn't getting onto the canvas to dry it out, in fact storm covers on for weeks would make it worse and at that price it requires the classic "Tell 'em their dreaming" .............
Scrub the bed ends down with warm mild soapy water, let dry well and truly, then spray with the waterproof solution that you use on Drizabone Coats, not the pressure pack stuff, the liquid stuff that you put in a spray bottle, spray that so its nice and damp then let it dry really well before you fold it all up............... If the mould is really bad it may bleach out with the sunlight but don't use bleach or chlorine products or anti mould stuff on the canvas, just warm soapy water, scrubbing brush, if gets too soapy then rinse and let dry in the sundry it really well, good air flow is a must, then soak in the waterproof juice and dry..............