I keep 2 boards outside.. on the south side of the house under the eaves.
So they don't lean against the house (termite protection) I installed 2 upright 20mm galv posts using a flange to fix to the concrete and installed end caps at the top. See here:
www.bunnings.com.au/products/bathroom-plumbing/plumbing/pipe-fittings/galvanised-pipe-fittings At the top and bottom of the posts I rivetted a metal loop. Also covered the posts with pool noodles.
On the ground i layed that thick rubber mat (sort of thing used for playgrounds.. from Bunnings).
This allows for 2 boards, one each side. Use 2 ropes with hooks at top, tied to the bottom loops.. super quick access/return (hook into loops at top of posts).
To protect them I made a simple cover from heavy duty tarp... with a plank of decking timber to weigh it down - the length of each side (just wrapped around the timber and gun stapled on).
This has kept the boards in as new condition and super quick and easy to access. Plus I can hose them off after a session in the stand. Have been using this setup for 5 years and use a SUP daily.
Originally i just kept them in their board bags but they deteriorated significantly overtime, which suggests the ambient light and occasional rain is degrading them (the bags).