Single Car Garage

Single car garage built probably 50+ years ago. Structurally sound. Just replaced the wood foundation. I am worried about the trusses though.
Length of the garage is 20' and width is 15'. There are 4 trusses, except for the ends. There is no real ridge pole just a 1" board used to help join the rafters together.
Despite it carrying snow loads over the past 50 years it looks as though it has never been used as storage space (between the bottom chord and the roof. I am desirous of using the space for some storage, nothing very heavy. Any suggestions on extra truss chords and other members that I could add to beef up the load capacity?

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