Hi John,
A suggestion.
Before you reassemble it you might like to clean the threads on the tank retaining bolts with a die nut.
I did this today as the ends of the bolts were quite rusted.
The die nut is a 10mm x 1.5.
I also found one other thing on my car. The steel fuel line into this area is often rusted but hidden from view until now. It is just a short right angled section in this area. Hydraulic hose guys have the tube and tools to make one for you.
regards,
Jolyon