You'll be fine changing tapes on the beach or at sea. The tape deck works in ambient air and isn't sealed off in any way. Dusty enviroments are more of a problem, and in these conditions it's worth loading a tape in clean air and taping up the door aperture.
As for skylight filters I'd say (again) don't. They make your preset white balances wrong, they add two air-to-(unclean) glass surfaces, they increase flare (and will do so dramatically if you don't use the hood) and are quite simply not necessary. The lens hood is far and away your best protection.
tom.
It's FCE v1 so I probably need more software too.
I think you'll need to upgrade to the latest version (4) - I don't think v1 does HDV. But be warned that the newer versions no longer include Compressor. Things like ffmpeg-X (free, good but complicated) and VisualHub (for general stuff - shareware) are good alternatives. Or On2 Flix Std (commercial but cheap as chips) if you need Flash movies.
http://www.ffmpegX.com/
http://www.techspansion.com/visualhub/
http://www.on2.com/index.php?387
VisualHub is probably the quickest easiest way of getting good results.
IIRC, Final Cut Express sucks in your HDV as 'Apple Intermediate Codec' which is easier to edit with than HDV, but it's not as efficient in storage terms. An hour's worth of HDV would be about 13 Gigabytes. FCE will convert it to AIC which uses approximately 4 times the disk space (52 Gigabytes per hour). But LaCie 500 GB disks are pretty cheap these days (I have 28).
You will want at least 2 Gigabytes of RAM!
Tom's right, forget about filters, just use the lens hood. And avoid changing tapes in dusty conditions. If it's really dusty or salty, tape up the compartment first.