Sorry Matt, they should have also told you about truss construction.
You should not have any storage between them either. A roof truss is a system, and if you stress any part of the system, holes, cuts , modifications or weight where it is not supposed to be, you could end up with failure.
I would find somewhere else to store things. A light box of wreaths or ornaments may be OK, but for an accumulation of heavy stuff, I would find another spot.
Also if you are in an area which needs to be insulated, you will not get it with a 2x4 worth of space.
Welcome to the forum.