Found rust under the battery. Mostly surface rust although there was some starting of "pitting." What technique would you, or have you used to repair this problem? Also, there was no plastic battery tray under the battery. Should there be one?

I used steel wool to clean up as much of the surface rust and take off any chipping paint. Then I used rust desolver to clean the spot further. Next, I used two coats of rust changer (says that it changes rust to a "black paintable primer"). That has dried for 2 days now and I plan to coat the area with flat black Rustoleum Barbeque Pit Paint (says it withstands higher temps than other paints).

Do you have any other suggestions? Should I take the car to a rust proofing place? body shop? or what?

 

IMHO sand it down (which sounds like you already have) then paint it with a "zinc primer" then paint.

 

The question is was the rust due to acid or just knocks that chipped the paint? It is a little late now, but you should have put on some baking soda to neutralize the acid.

All the stuff you put on may have done a fair job of neutralizing anyway. One thing though is that the rust converter stuff does not hang onto metal very good if there is not sufficient surface rust giving a good tooth. In other words, put it on clean metal and it will scrape and peal off fairly easy. Sounds like you may have cleaned the area a bit too much for the rust converter. If it didn't turn jet black, there wasn't enough rust. So you may want to play around removing that a bit with a razor to see how well it is stuck.

Anyway, paint it up with some gloss paint (gloss so water and crud won't hang on the flat paint so easy, and don't worry about temperature as it is fairly cool in that area). Put primer on the spots you scrape down to metal on the rust converter scrape test. Check the repair every 3 months to see if the rust and/or acid attack is going to return.

No need to go to a body shop now, you have caught the problem and with some regular checking you will see if it is going to return and can deal with it.

 

It sounds like you got to the problem before it got out of hand (unlike my S2). Suggest that just to be sure things are sealed up check the battery box area from the inside (top of passengers foot well) for signs of leakage. --Roy--