I have a few holes in the back of the engine compartment from rust caused by clogged drain under the hood.
There's a little detail about my situation here: http://www.peachparts.com/shopforum/showthread.php?t=221588

My problem was worse than I thought once I looked under the battery trey (surprise!!!)
So, here's a picture of the afflicted area. Someone suggested originally that I patch another hole with fiberglass cloth and epoxy resin (same problem on the driver's side).

I read lots of things about how rust improperly dealt with will always grow. In haste I sanded down the metal facing skyward, rinsed with alcohol, dried, and sprayed a few layers of rust converter on the spots around the hole. My plan was to use the epoxy resin/fiberglass cloth trick on this spot.
Here's my concern, I'm not terribly concerned with keeping original design motifs the same, but I don't want to do a shoddy job and leave the situation to deteriorate in a few years.
Can anyone give me any pointers? There's rust on either side of the metal. Should I just sand, use the rust converter, and then what, prime? Should POR-15 play a role in my stategy?
I just want to be thorough.

Grind to bare metal and take it to the welding shop. Have them put in a bit of metal and then spray some Chassis Saver on it. That will fix it.