A few weeks after taking my 85 Transporter/Westfalia out of winter storage I
am getting a constant whine from the fuel pump. Previously had two short
whines from the pump just after turning the ignition on (1-2 seconds each) -
then silence.  Now it whines all the time. I'm assuming that the right
(cheapest) course of action is to change the fuel filter which is exactly
2yrs and about 25,000 km old.

If this doesn't cure the problem what next?

Should I be suspecting the fuel tank at this age (15yrs) and 208,000 km? I
don't believe it has been changed or lined or anything.

Any advice on next steps?

If it turns out I need a new tank,  I understand from passing interest in a
recent series of posts that the Bus Depot has new metal aftermarket one at a
reasonable price, and that there is no such thing as a plastic one?