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Which Rustproofing inner panels

Going to spray inside the inner door panels , inner rockers, box wheel arches ect..
On my new Ford F150(aluminum). Debating on which to use Fluid Film or Amsoil Heavy duty metal protector
(MPHD). Any thoughts?


Active Member
I use cavity wax. 3M Rust Fighter. They have a wand sprayer that attaches to a schutz gun.

As far as I know the OEMs use cavity wax too. Wicks into seams etc and does not harden and crack.

Used similar products(to 3m) from Kent's cavity protector to Rusfre cavity wax.
Amsoil Mphd is a similar product(but better priced) to those, sprays and smells very similar. Goes from liquid to a wax like film.
Fluid film is a different animal, that creeps and thickens, but doesn't dry. Either will work I'm sure.
I probably wouldn't use Fluid film on outer frame rails and such where you would rub against it when working under the vehicle.
Probably be messy as it stays somewhat wet. But for interior panels that wouldn't make much difference.
I have a case of each Amsoil and Fluid film. The Amsoil is what I will use on the frame, axles, back side bumpers, suspension ect..
Up in the air on the inner panels yet.


Top Banana
I've only experimented with FF so far. It's non toxic oily forever lanolin base. Smells fine.
Bought 2 gallons & cheap airless paint sprayer to soak my 3 car bottoms.
It's not wax at all. Oily forever, creeps into every pore.
Does wash off where water spray from wheels gets it so it's annual reapply in places.
Gotta say it doesnt turn back time but rust pretty much halted.
I imagine brake line fittings and such won't be a struggle in future to loosen.
I would've preferred wax in places but not complaining.

Used $11 hot plate & $1 tray to slightly heat it before pouring in sprayer.
Gallon can stuff looks thick & turns to water with heat.

Don't spray in door drain holes cause mist will get parts that rub glass.
Pull door panel & brush it on or gentle spray with tube.

My 2c
I use the 3M Rustfighter I as described earlier with the special gun and wand for the inside of rockers. For the inside of outer door panels I use 3M Body Schutz to duplicate the undercoating manufacturers used on older cars in this area, but I suppose the Rustfighter might be better for this if you suspect the door panel might get damaged at some point and need to be repaired with PDR.