You have an Atwood (thermal fuse)
You have a 10 gallon combo (gas/electric) model
Your MH is 2004 but sounds like you have one of the last version GC10A-3E
That one is last of the models that used separate controls for electric & propane
120V AC set of t-stats and element on backside of water heater tank
12V DC set of t-stats in outside compartment for propane
The 'drawn pan' IS available.....Atwood 93871
You would also need the ring/gasket kit (metal seal rings that secure pan to tank)....Atwood 96010
You would have better luck repairing fallen floor/support by pulling water heater completely out so you could remove rotten/damaged wood and rebuild it
(only reason for tank to drop)
Also if you do want to replace the whole water heater the GC10-4E IS the replacement....fits same opening as 3E and previous models.
Per Atwood
The 3-E and 9-E are no longer available, if an entire water heater must be replaced it will be replaced with the new 4-E or 10-E.
There are no changes in the physical dimensions, but a wiring
change will be required.
Wiring change is the use of Common DC circuit to power both on/off switches and the 120V AC going to the DC Relay before going to the element