Pretty basic, load up your favorite internet browser, mine personally is Internet Viewer (not Internet Explorer, it's something completely different), but go to: https://www.saintsrowmods.com/forum/threads/first-person-camera-experiment.1577/ Scroll down the page until you see "Attached Files", click both, this will download both files, and you need both! After clicking download you should end up with SRTT_fps_experiment_0.4_BMS.zip and fps_experiment_0.4_patch BMS.zip.

This is pretty simple to do! Go to C:/Program Files X86/Steam/SteamApps/Common/Saints Row The Third, and unpack the files in there. Note if you don't want your character to have a head to pop in and out of your camera, follow this order, unpack SRTT_fps_experiment_0.4_BMS.zip first and the patch second. This will play a crucial part later...

This may sound really strange to most of you, but you must take off your character's clothing entirely for their body to disappear... like I said really strange but I'm being honest here, if you don't want your character's head to pop in and out of the camera, unclothe your legs. For just a floating set of arms take off the top your character is wearing too. And DO NOT wear hats! It's a bad idea all around... And remove hair...