Have a mail consolidator manage your post and then have it delivered to whatever harbour/marina you are visiting next.
By consolidator, I mean someone who will act as a post box.
I think from an earlier post, Geoff Pack's widow (Geoff was editor of this august organ) still runs "Ship to Shore" which provides this (and other) services to long term cruisers. Mr Jermain will doubtless confirm or deny.
<hr width=100% size=1>A pontification from the Panjandrum of orotund bloviation AD2002
Ship to Shore, was started by Geoff Pack and run for a while by his wife, Lou Lou but it's now run by Michelle Miller, tel: 01962 868642, email michelle@Shiptoshore.co.uk, web Shiptoshore.co.uk.
She acts as your shore base for forwarding post, ordering spares etc.