I bet that panel has a hinge on the top to lift up the panel. My coach has latches on the bottom to lift it up but others have said theirs had screws to hold it down.
No the tank does not have to be removed to replace the sender unit. The hole in the top of the tank is larger than the sender portion that extends into the tank so the sender can tilt to lift out.
Caution: make sure it is clean around the top and by all means
take pictures so the wires can be reinstalled correctly. I called Joel at Centroid and he made me a new unit exactly like the original one ($90). Some have said the wires were not color coded but mine were.
Here is the web site for Centroid:
CENTROID PRODUCTS - Computerized Tank Display - Electronic Senders - capacitive fuel gauges
Good luck
Dave