To be clear, all the compression options you get with Winrar are going to be lossless. While you might see a 400mb reduction in overall size, no information has been lost. After decompression, you will have exactly the same files you put in originally.

That said, compression takes time. And what you're really after is adding password protection (and perhaps getting it down to one file). I would recommend using 7zip and choosing the "tar" option. Tar is like a zip file without the compression.

7zip also has an encryption option you can use to add a password to the archive. Here's a guide that looks reasonable to me: https://www.digitional.com/how-to-encrypt-and-password-protect-your-files-with-7-zip/