I don’t think so. As Mike says a Barn brings all sorts of benefits, but I do not believe you have to have one.
I had significant deck work to do on Helene and for that work I created a scaffold and tarpaulin ‘shed’ which worked brilliantly. See below. It cost about £1000 initially but has a secondhand value as well at the end (mine is actually loaned for an Airstrem renovation). See below for pictures of mine, and other people’s…
And once you have completed any necessarey renovations and got your Atalanta in good shape, a well fitted cover over a ridge pole (NOT the mast) with frames (polypipe or similar) to hold the cover off the woodwork will keep her in good fettle.
Chris Green had a similar construction for Kerry Piper.
And A17 Gambol has a very fine wood/canvas tent described in the 2013-14 Bulletin, Page 14 onwards.
Of course, the ideal would be to build yourself a Trevor-style Boat Shed, or go one better and pitch for a Murray version