You still need to use some blast weight in a resin bait. Sometimes the hooks and hangers are enough balast, but usually a little weight is required to get the proper action.
I have mixed straight resin and poured the lower third of the bait and then mixed resin with balloons to pour the upper 2/3rds of the bait. It works pretty good for a large topwater bait, but you must do it quickly so the two halfs adhere together and you don't get a large seam.