Is there an acsess panel under the back seat for the fuel pump and sending unit

I don't think so according to the literature:
REMOVAL & INSTALLATION CAUTION
The fuel injection system remains under pressure, even after the engine has been turned OFF. The fuel system pressure must be relieved before disconnecting any fuel lines. Failure to do so may result in fire and/or personal injury.

1. Relieve the fuel system pressure. Refer to procedure in this section.
2. Disconnect the negative battery cable.
3. Drain the fuel tank, then remove the fuel tank from the vehicle. Refer to procedure located later in this section.
4. Thoroughly clean the area surrounding the sender snapring. Compressed air may be directed around the seal. CAUTION
   Safety glasses MUST be worn when using compressed air to avoid eye injury due to flying dirt particles!
   
5. While holding the modular fuel sender assembly down, remove the snap-ring from the designated slots located on the retainer. WARNING
   The modular fuel sender assembly may spring up from its position. When removing the modular fuel sender from the tank, be aware that the reservoir bucket is full of fuel. It must be tipped slightly during removal to avoid damage to the float.
   
6. Remove the external fuel strainer.
7. Detach the Connector Position Assurance (CPA) piece from the electrical connector and detach the fuel pump electrical connector.
8. Gently release the tabs on the sides of the fuel sender at the cover assembly. Begin by squeezing the sides of the reservoir and releasing the tab opposite the fuel level sensor. Move clockwise to release the second and third tabs in the same manner.
9. Lift the cover assembly out far enough to detach the fuel pump electrical connection.
10. Rotate the fuel pump baffle counterclockwise and remove the baffle and pump assembly from the retainer.
11. Slide the fuel pump outlet out of slot, then remove the fuel pump outlet seal. To install:
    
12. Install the fuel pump outlet seal, then slide the fuel pump outlet in the slots of reservoir cover.
13. Install the fuel pump and baffle assembly onto the reservoir retainer and rotate clockwise until seated.
14. Install the lower retainer assembly partially into the reservoir. Line up all 3 sleeve tabs. Press the retainer onto the reservoir making sure all 3 tabs are firmly seated. NOTE: Gently pull on the fuel pump reservoir from retainer to assure a secure fastening. If not secure, replace the entire fuel sender.
    
15. Attach the fuel pump connector.
16. Fasten the CPA connector to the fuel sender cover.
17. Install a new external fuel strainer.
18. Install the modular fuel sender.
19. Install the fuel tank in the vehicle.
20. Connect the negative battery cable.
21. Pressurize the fuel system and verify no leaks. Fig. 1: The fuel pump/fuel sender module assembly is mounted in the fuel tank