If you are wiring into the power seat circuit your electrical device will be protected up to the amperage of the circuit that the power seats are on. ...sorry no manual at hand to tell you what that circuit is rated at. An extra fuse of lower amperage would protect your electrical device more than the circuit would by it's existing fuse.
When I do this mod, I will run a new wire from the fusebox, or even the battery to the outlet. Max amperage can only be achieved this way.
The seats have a pretty high amp fuse. I run my inverter off of that power source all of the time and it holds up very well. In fact, it was the inverter that made me install the outlets there. It would blow the lighter fuse.