What's the rest of your roster look like? Are you deep at WR?
Charles is a risk because of the overall offensive level of play. However I'm sure you know the insanely favorable schedule for Charles hence your desire to do this deal. Assuming Crabtree is essentially an extra WR come playoff time, I'd do it and go for Decker. Good match ups in the playoffs and has been as consistent as Megatron has been inconsistent. Megatron is just the name, not the #1 receiver he has been for a couple seasons now.
If you are dealing 3 starters with nothing behind Crabtree...I'm not sure just because of the risk with Charles. Mathews and Bryant are far from solid studs though, so again...for me it'd depend on your teams overall situation.
Here's mine: viewtopic.php?f=18&t=529083