2.5inch spinning disks max out at 5Gb, so for anything bigger you'd be looking at spendy SSDs or 3.5inch drives.
3,5inch won't be straightforward, but not impossible, you could use a USB to SATA lead, and feed the drive the 12v it needs from whatever supply you have on the boat.
The basic premise here is that people with these lost episodes 'stole' them from bins after they were thrown out by the BBC, so don't want to admit this to the BBC, as they are worried that the rather large corporation that the BBC is, will take them to court and win.
I needed to burn some Samsung NUON games recently, and I found that an old version of Alcohol 120% worked fine with the unusual format needed, none of the 'current' apps I tried would play ball.
So many options here;
Just press CTRL+D
or use gmail and tags, then archive the messages so they don't 'take up space'
or a notepad text doc in dropbox
or google keep