According to at least one table on dissimilar metals, aluminum, dedpending on the alloy, would produce 0.75-0.95 V and steel would produce 0.85 V. Under severe conditions, ie salt water, the difference should be kept to less than 0.15 V; under agerage conditions, ie humidity, a maximum difference of 0.25 V is OK. Looks to me like we are pretty safe without unless you drive in high salt conditions.

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Gary & Edie
North Idaho
1988 28' P-30 454

Just for comparison, check out the fiberglass Pace Arrows of the past 10-15 years. I have not seen an older one without wall delamination, some very severe. This can be seen by looking down the sides at the bulging and buckling walls. The fix for delaminated walls is to replace the entire wall! My old 85 Barth Regal has its exterior aluminum skin as straight as an arrow.

Not to be redundant, but I have only seen this corrosion we are speaking of on the compartment doors. Has anyone one had a severe problem on the body. I just have never seen it. My rv guy said to repair the door, just cut out the bad part and replace it with some glass cloth and epoxy. I did that and it looks really nice. However, the paint I bought doesn't match too well.

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Re: Where to find zinc anodes - they're a standard marine item, available in various shapes & sizes through any marine supply outlet.

In view of the general lack of evidence for corrosion anywhere except in storage compartment doors, even on aged Barths, installing anodes seems like overkill.

I have corrosion on one locker door only, and the pits/perforations are far away from the edges of the panel. I haven't explored the matter closely, but I don't understand how we could have galvanic corrosion in the middle of an aluminum panel inserted in a welded aluminum frame. Perhaps there's some critical difference in the alloys used for the skin and the frame, or the skin and the substrate underneath, or maybe there's something wrong with the quality of material used in the door skins..

I have about a half-dozen holes, all small enough to patch with bondo, or if I want to get fancy, epoxy.

Anodes are not going to be effective unless you are operating in 12 to 18" of standing water.
The electrical potential between the steel and aluminum or other dissemilar metals is not going to be a concern unless there is moisture available to provide a pathway for the ions. I have an aluminum panel under my small trailer that essentially covers the bottom of its little world. The trailer shows no pitting or other damage from the dissemilar metals in contact and I will guess this is due to the panel. It is keeping moisture intrusion to a minimum and dirt build-up eliminated. Without the build up of dirt there is no retained moisture in crevices and joints where the different alloys are mated.
I would guess this is the general method used by Barth, eliminate moisture retention and dirt build-up in mating surface areas. I also would expect this to be the cause of the failure of the aluminum trailer with steel springs and shackles.
Mostly speKulation on speckling and pitting that seems to be of little real concern.
Tim

Well, the corrosion on my Regency is almost all in the steel areas under the edges of the aluminum skin and the compartments. Some of the aluminum... the under the skin parts back in the engine compartment... is showing signs of minor corrosion, and driving through most anywhere in the northern tier in the winter will spray the frame areas (particularly the engine compartment) with a salt solution... Aluminum, Iron, and salt! A pretty "juicy" combination. I was leaning into my engine compartment, holding onto the frame, and brushed my cheek against the aluminum framework of the compartment door and felt a very weak charge. I licked it, and sure enough, a volt or so.

My rig has lived in the North East so perhaps it's an extreme case. A testament to the Barth construction, though, as it's still sound and sturdy... just enough of a concern for me to want to attach a few zinc sacrificial anodes around the framework. If I want it to last another 20 years I'll let the zinc's corrode instead of the coach.

I spray any areas where steel and aluminum come together with LPS 3. It also works well on battery and other electrical terminals subject to corrosion. It flows on as a thin liquid and then sets up as thick, almost wax-like grease.

Boeshield is another good product.

For already rusted areas my treatment begins with EXTEND. It converts the surface oxide molecules to a polymer, stopping the progression of the rust. Then I paint with rust-o-leum (though I hear POR-15 is GREAT) and spray undercoat. That EXTEND is pretty cool stuff. I worked at LOCTITE for a bit years back, and we'd go to product training sessions in the labs. EXTEND's polymers actually molecularly bond with the oxide molecules, truly converting the surface of the metal to a polymer compound. Not just a coating. Neat. Once treated, then top-coated, it won't rust. I've had it on treated metal parts for 10-15 years, the rust simply never comes back.