RicodJour wrote:

If he's just looking to add storage capabilities (floor load),
why does he have to touch the roof? He could ignore the trusses
and install floor joists next to them, but if he doesn't have a
center support wall, he probably can't do that.

Look what the original poster (OP) said:

"Currently I'm busy fastening 3/4" plyboard over the ceiling
rafters (so objects to be stored won't crash thru the drywall
ceiling)."

So we can assume that the rafters are strong enough to support someone
wiggling around putting plywood down?

3/4 plywood to tie the rafters together will certainly give some
additional strength to the load-bearing capacity.