Encrypt FAT USB drive under El Capitan (10.11) I have a USB drive I would like to encrypt. It's formatted in FAT (for use with Mac &amp; Win) and I can't seem to find a way to encrypt it as:

FileVault doesn't encrypt FAT.

TrueCrypt can be installed after modifying the installer but doesn't run under 10.11 for me (library file missing) and there seems to be no solution, since TrueCrypt is no longer supported.

Is there any solution to encrypt the stick without resorting to using a different computer?
You could look into VeraCrypt which is the open-source successor to TrueCrypt and exists for Windows, OS X, and Linux. It can also open existing  TrueCrypt containers. https://veracrypt.codeplex.com 

Like TrueCrypt, VeraCrypt can create an encrypted CONTAINER FILE which is like an DMG or ISO image file and can be copied, so it would fit on a FAT32-formatted USB drive as long as the file size remains below 4 GB, as FAT32 cannot contain individual files larger than that. For this a container file you can choose between FAT, exFAT, and OS X Extended as the internal format. For maximum compatibility between Windows and OS X, FAT is the right choice. ExFAT can take files larger than 4 GB and is supported by Windows XP, but it is not supported in OS X before 10.6.5 Snow Leopard. 

Finally, you can also use VeraCrypt to create an ENCRYPTED DRIVE VOLUME, so that the whole USB drive or a partition itself is encrypted. However, VeraCrypt doesn't encrypt existing files directly. First you create an empty  encrypted container file or drive volume, then you copy your files to it.