You might want to consider coating the inside of the tank, and paint the
outside with a good rust preventive paint.  See
http://www.eastwoodco.com/cgi-bin/sgsh0101.exe for some products to
consider.  A friend of mine recently used this kit on his 1940 vintage
tractor's tank, which was very rusty on the inside.  Worked great for
him.
--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia w/2.1
'65 MGB (Daily driver since 1969)
'74 MGB GT (Restoring sloooowly)

Assisting on Restoration (and spending OPM):
'72 MGB GT (Daughter's)
'64 MGB (Son's)

Stripped and gone but their parts live on:
'68 MGB, '73 MGB, '67 MGB GT