just finished up today spraying down all 4 doors, bottom panels,
inside wheel wells, trunk, exhaust, some areas of engine bay & underside
of engine and surrounding areas using CROWN rustproofing chemical oil.
took it out for a drive to burnoff some oil spray on the exhaust. and finally
I'm done with it and ready for winters fury.

Yep. Once the holes have been drilled by Krown dealer for the first time, I use the RustCheck red can in the panels and doors trunk and hood every year. The RustCheck green can gets sprayed under the car.

Personally I am a big fan of this product. I used to apply it to truck frames when I was a toyota tech. It is nasty and slow to dry, but when done well and allowed to dry it looks good and doesn't harden. It dries to a wax like finish so it doesn't flake off.

https://www.amazon.com/Noxudol-N300D.../dp/B00L9EB1F4

Think about it from this standpoint. Toyota specified it for official use on their vehicles to deal with corrosion issues on their truck frames. If a top five automaker considers it to be the right choice for their products it is some pretty good stuff.

just be carefull not spray your rubber mouldings or any inside
door frame rubbers using rustcheck because they will warp from it.

Can you spray this on a spot that is currently starting to rust to slow the rust down?

There's a spot on my hood that's starting to rust and has caused some small paint bubbling next to it

Yes You can spray a rusted spot down using Crown all its going to do is
slow the Rusting process down. as far as spraying down paint bubbling
I'm not sure what it looks like on your car. but I would spray it too...
I sprayed all my vehicles down using Crown and just recently went to

do an oil change on the civic while underneath it I noticed everything
I sprayed down there back near the end of November last year being
in November 2016" was still very moist and oily I'm pretty impressed
with Crown. Crown says there chemical oil spray will stay on for a full
Year. so Yeah...! its got my thumb up.