It's very easy now that RGL has been released with the auto patcher, hop on xbins and go to:
xbox360>development>rgloader

Download these two zips:
_RGBuild2_Beta0v170.rar
14699-filesystem_0v170.rar

Then this is straight from the readme:

Copy Filesystems & loaders folder into the rgbuilder root.

Create a folder 'Filesystems' on your xbox hard drive.
Copy everything inside of 'hdd-filesystems' into the new 'Filesystems' folder.

The Filesystems folder should have '14699-dev' inside it now.

There is no need to run xextool or hex edit any of the files, they have been prepared for you.

Read the README of rgbuild.
Edit build.bat with your cpu_key.
Put your xbox nand image into the root next to build.bat and name it 'nand.bin'.

Run build.bat.

Make sure you put the folder on the root of your xbox hard drive, not usb

Also you might need to apply another patch to the 2bl if you've updated to the 14719.

If you have, once you extract your
_RGBuild2_Beta0v170.rar
Go to:
_RGBuild2_Beta0v170\patches\2BL

Open the file thats in there and add this code to the very end of the file: