With a Fink truss, it will make little difference where you place a distributed load.  For applications such as yours, I would rather see the load near the center so that as overloading occurs, deflection becomes a clear indicator of a problem, whereas if loaded near the ends, a faster failure could occur in overload condition.

Most of these trusses are designed for either a 30 or 40 psf total load, as well as for wind loads.  While you will be adding dead load (essentially) which normally helps negate some wind load conditions, in this configuration, it will add to the wind load, so you have to be a bit careful with the amount of load you put there.  I would not put files, boxed paper, etc. but light household should be OK.  The floor will actually help the stiffness of the system and make it work better together, as long as you don't overload the entire garage area!  If you want to get a little extra warm fuzzy feeling about it all, you can add a plywood diaphragm to the sides of the truss or you could double the bottom chord.  I would suggest that you add nails to the truss plates, no matter what else you do with them.  This helps the long term performance of the truss and will reduce the shrinkage of the wood/plate interface which significantly reduces the load capacity of the plate connector.

Putting a floor in an attic space is tough work!  Have fun and drinks lots of water (save the beer for afterward!)

Good luck.

My loft has got glass fibre insulating quilt - wear a disposable overall and a face mask - glass fibres can irritate your skin. Be carefull how you fix the boards down to the ceiling tie - you may be nailing blind and splitting the timbers - avoid nailing in close proximity to the gang-nail truss plates.

Use common sense when loading out the trusses - the loft hatch size will normally stop you from putting to much bid stuff in the roof - but try to spread heavy stuff ( suit-cases full of out-of-season clothes) about a bit and dont stack them on top of each other.