Roy,
The weathering techineque could be used on any model subject, only thing about the remark towards Tamiya, is because we had some laying around the shop at the time, [left over from various repairs, when I was working there], you should be able to use any spray paint can or even sprayed through an airbrush.
With WW II armour I'd use a dark metalic [like gun metal] as the base coat, in relation to the Lvt 4. My sujestion would be the gum metal colour as a base coat and work from there, once the top cam and decals are finished and sealed, just apply your interpretation of the chipping effect.
I know in the days when I drove M113's, the scratches and stuff we got in most places along the sidewalls, would show the aluminium base metal. The heavier the tree branch the more scratches and sometimes the bow plate would show signs of wood showing where the paint had been scracth off.
Wethering Techineque of Catalina aircrfat:
This was how I did the weathering to the 'Cat' apply the silver base coat and let dry over night, mixed my Black paint for the lower main wing and fuselage on a 1 to 1 basis, when this was finished, both the Grey and Blue cam was applied again mixed too the same ratio and left until the paint was touch dry to handled, I then applied the decals to the model, using a decal solvent to sit them down, once that was dried, I then rubbed the Black from the lower wing with an emery board.
With the fuselage I repeated the same rubbing principals to both the paint and decaled area's, then repeated the same process on the upper main wing, I used an Acrylic thinner to wash the model of excess shavings from the emery board and applied a coat of Dullcoat to the entire model, when that was dry I them used a medium grey pastel for the canvas area, of the main wing and a darker grey black mix for the canvas on the tailplanes and rudder, the exhausts stains are amix of black red brown and dark grey pastels, I then sealed the pastels with a sealer [workable fixative spray - most artist supplies sell this spray sealer].
Applied the Dullcoat to the model and allowed to dry before fixing the trailing antenia array, from wingtip to rudder to opasite wingtip and from centre main wing to rudder.
The PBY Catalina model I had built, was based on this this wartime photo, as this was the instruction of the Officer Training School, this model was built for.
I've heard of modeller's using salt as a weathering technique, but I have never tried it on any of my model subjects.
Hope this helped a little.