I see all the top people using covers to keep their carbon masts away from UV light, but is there an alternative option for keeping snails, sap and mould off my aluminium mast whilst it's in storage? The problem is more the halyards than the mast itself, though cleaning the luff groove of leaf muck is dull work.

Dear Mags A shed is good.
It has come to pass that there is a connection between mast bags leading to trapped dampness and croshen that eats away at the jib sheath box lower flange also building under the mast wall and the jib box inner edge coursing the mast wall to bunch and splitting, resulting in a sort of cheese wire job as the boat travels up wind and the jib halyard travels down with the now mobile sheath box, but I have not noted snails.
It should say that mast left standing on the boat in all weathers in the dinghy park appear croshen free.
Mr. Chipstow is in carrots with Allen Br. Seeking an alternative sheath box material.

I have a garage roof, but the garage is not big enough inside. Tried standing it upright against the house, but the mast is taller! Wifey not happy and wants the 'unsightly' object removed from the garden...

One solution is to cut a hole in the back of the garage wall and fit a length of wastepipe long enough to accommodate the mast. How viable this is will depend on how much too short the garage is!

3 options really:

1.Extend the garage
2. Put mast in Lounge - warm and not damp!
3. Buy a house with a bigger garage

I cut a hole in the bottom riser of the staircase, and had it in the hall and projecting through into the understairs space. Actually, that was with my ex.; I wonder if..........

Mags, North have just started making mast bags and have a design for the Merlin mast. And it's breathable I think which should stop the croshen...  speak to Dave Hayes at the One design loft...
Have ordered one for my B14 mast...

I have not come across the word 'coshen' before - so needed to educate myself. I put the word in to Google. The first few entries were all related to the art world - the something more promising  -  a cross reference to the Merlin Forum.  So that helps!

croshen = corrosion?

Just a guess, is it mobile phone texting language?

It's just the local dialect. Surprised nobody has noticed 'in carrots' - unless you all understood that bit?

Painting the mast white (or any other colour) will protect the carbon from UV damage

Painting the mast white protects from UV damage NOT corrosion!  Corrosion occurs as a result of electrlytic reaction( basically 2 different metals(or 1 metal + Carbon) plus a fluid( water ) produces a battery and this causes the metal or carbon to degrade.  So a dry stored mast out of light is best!

I store my hog stepped mast diagonally across my double width garage and it fits in with a bit to spare (so I can get the door closed).
So extend your garage or I could rent you some space ;+)