Wheel well rust. What to do?

[Skamper1]

Removed wheels. Found a lot of rust everywhere. Am going to pull hubs, repack bearings and check brakes. What should or could I do to the surface rust? Was thinking a light power wash and cleaning. Hate using Ospho because it is like painting with water. Not sure a I can spray it on with a bottle sprayer. Three inch crack in wheel well. Can I leave this for now or should I seal it as a temporary fix? Any suggestions appreciated.

[Skamper1]

Pictures did not load. Will try again.

[Lumatic]

Surface rust is normal. Depending on how deep it is there may or may not be a problem. I cleaned the rust with a wire brush attachment on a drill and got some spray can undercoating. I "liberated" a couple of smushed orange barrels and saved them from certain destruction. I used the plastic and pop riveted it inside the fender well. This is one place on an Airstream where silicone is a good thing. Did this patch job several years ago and no leaks yet.

Don't have a clue what Ospho is.

[ROBERT CROSS]

The frame area around the wheels looked about the same on our "63".

Used THIS...it looked pretty darn good 5yrs later when we sold it.

I used the spray-on

[Skamper1]

Well, here is plan A: Brush off loose rust, phosphoric acid to neutralize rust and then use spray undercoat which has a primer. Only concern is to just treat wheel well or anything I see on, near, around wheel well enclosure? Except for crack pictured, all seams seem to be intact.