A video of your transformation would be great! First, al lot of that surface will clean with soap and water
The rustmort is made for bodywork, to pull rust to the surface and kill it. On white surfaces you will draw it to the surface and rinse it off.
Best way is to spray it on evenly, scrub on the darker areas while letting the chemical work. Rinse, dry and spray again where needed.
Try out the back first, don't let it run down dry surfaces, make sure it is sprayed evenly then rinsed. Keep a close eye on decals.
I don't know if this will be a winter project, as fast as you have been moving on this thing,it will be ready next weekend.