Rust in the lower rear cab corners. The third brake light can leak, water runs around the window inside the cab, lays in the corners, and causes rust.
V8 models can get cracked exhaust manifolds.
Check the HVAC controls for the temperature to change and air to come out in all positions. The blend door actuators can go bad with age, not a big deal to replace.
Otherwise they're pretty much tanks. Change all the fluids and filters and drive on.
On 07's the release for the front storage compartment in the bed is under the driver's side bed rail, which is different from 08-10 which have a simple knob on the lid.
I owned an 08 Sport Trac until three weeks ago.