Well buddy let me help you out. Since I have a system that does exactly what you're asking for on Debian Linux. I set it up a long time ago so I may be forgetting something.

Only an idiot would do "security stuff" blindly without researching on their own and my personal security hangups do not necessarily match anyone elses on the planet. So thats the disclaimer. Given that disclaimer:

Assuming a sane linux like Debian, as root "apt-get install fuse encfs". Make sure encfs shows up in the "lsmod | grep encfs" list. Make sure your username is in the fuse group, so "man adduser" or hope "adduser jareds fuse". If you add yourself to a group, you're not "really" in that group until you log out and log back in. That sounds like an awful amount of work but its really about 5 minutes. (and I do groups in LDAP, you probably don't, and I don't remember if this is proper syntax for old fashioned local files)

In yer ~/Dropbox, make a directory encfs

In ~/Dropbox/encfs make directories for your stuff. Lets be uncreative and make a directory called passwords to store passwords lists and things

Make a script in ~/Dropbox/encfs called encfs.sh and chmod a+x it so you can run it.

#!/bin/bash

# This script is ~/Dropbox/encfs/encfs.sh

# Dont forget to chmod a+x this script

# apt-get install fuse encfs

# make sure fuse shows up in lsmod | grep fuse

# make sure user is in group fuse as in adduser vince fuse and log out and log back in

echo We are now mounting your passwords directory aka ~/passwords

fusermount -u /home/jareds/passwords

encfs /home/jareds/Dropbox/encfs/passwords /home/jareds/passwords

exit 0

I'm making some assumptions about the locations of your home directory. You should be able to figure it out. I use AFS at home which makes for long path names. Others use NFS. Whatever. It seems self explanatory enough?

That unmount command will fail if its not mounted. Thats OK. The reason why this is necessary is if the system crashes or who knows what, sometimes the fuse mount gets stuck and can't be re-added by encfs. Annoying. But trying to unmount cures a stuck fuse mount.

Run it and I forget how you set your password. Likely it prompts. Been a long time since I set this up and I forget how to create. The script above is great for remounting an existing encfs, it is a somewhat edited version of what I use.

Anyway assuming you get it working go visit ~/passwords, and make a couple files. Don't matter what, just df > test1, free -m > test2 its all good enough. Go visit ~/Dropbox/encfs/passwords and see instead of test1 and test2, two filenames looking like line noise and the contents look like line noise. Edited to emphasize its one encrypted file per decrypted file, not a single giant file.

If you're ever bored, look at the xml file ~/Dropbox/encfs/passwords/.encfs6.xml So I'm using 256 bit AES with 1024 byte blocks, OK then.

Encfs is no speed demon. I wouldn't go putting 1080p high def video files on it. Then again I have no idea why I'd want to encrypt those.

(edited to add, I'm in "submitting too fast" prison, but to answer webmaven's question, wrapping in encfs also fixes the case conflict problem that dropbox has... you could presumably use UTF-8 filenames for all encfs cares, the encrypted filenames will look like 32 characters of line noise no matter what you name the file)