Diesel fuel tank for winter period

[Tiger Lily]

My diesel fuel tank is 50% full and will require approx 100 litres to fill up but I am unlikely to get the boat filled up this winter. Can anyone advise what measures I can take to prevent condensation appearing inside the tank. I am currently moored near Bourne End near Marlow

 

[dunedin]

Make sure the tank filler cap has a good o ring to prevent rain getting in.

Other than that I think the concept of filling tanks up pre winter has largely been debunked and many now consider it better to keep the tank low and fill with new fuel in the spring.