Truss modification for light storage

I have 24' single fink trusses on 10/12 pitch. There are 15 of them, I believe. They are built with what appears to be #2 grade lumber 2x4 (the webs are clearly stamped, I don't see grade marks on the chords). The designs for storage spans want a 2x6 Bottom chord or SS grade lumber on the BC (with M of E of 1.8MM). I want to sister the bottom and perhaps top chords of the existing trusses to allow for 25 live and 10 dead psf loads typical of storage. Both sides top wall plates are open to bear. I need a stamped approvable design for Springboro OH permit application. I can get 12' to 16' members into the attic access. I have a design from a PE that shows a fink design that works, and the clear triangular span in the middle of the truss is an adequate area.