Surface rust removal

[Mobilesport]

I removed my shower pan and underneath it is this 3/16" steel sheet  , it has 1x1 inch tubing welded underneath it so it will hold my weight , this steel sheet is removable , when I installed all of this a couple of years back I painted everything except this side that is rusted , I didn't expect water to get to it , the under side I sprayed with bedliner , 
So can I sand this rust off and prevent it from coming back or should I start out with a new metal piece and then just paint it?
The yellow stuff in the center is pieces of the carpet that got stuck when I pulled a piece of carpet out that was under the shower pan.

 

[BradKW]

I'd just sand it, coat with Corroseal, then a zinc primer, then solvent based paint. Or just replace it if it's easier...

 

[Mobilesport]

I'd just sand it, coat with Corroseal, then a zinc primer, then solvent based paint. Or just replace it if it's easier...

It wouldn't be hard because its removable but it comes down to which would be more cost effective , I found a replacement steel sheet for $60 , I gotta cut it to my size 
So it would come down to the price of 
$5 -----80 grit sanding disc
$ -----Coraseal
$ ------Zinc Primer 
$0 ------I have the paint.

 

[highdesertranger]

dang 3/16 plate. thats got to weigh a ton. I would take a wire wheel on an angle grinder get all the surface rust off. then use a rust converter product. the use something like por-15 to seal it. highdesertranger

 

[Mobilesport]

dang 3/16 plate.  thats got to weigh a ton.  I would take a wire wheel on an angle grinder get all the surface rust off.  then use a rust converter product.  the use something like por-15 to seal it.  highdesertranger

Yep , its heavy , unfortunately that blue part of that dropped down floor is also heavy , I pieced all of it together with metal I got from a scrap pile ,, same thing with my Under floor propane box but I'm ok with the Propane box being heavy , I wanted it to be solid , for my shower pan area it would've been nice to have some sort of a stainless steel pan exactly the size of that blue homemade floor pan but since I needed it a specific size I had to make it.
Propane box skeleton is 1x1 inch tubing --1x2 inch tubing covered with 14 gage sheet metal

 

[VJG1977]

If you replaced the sheet metal, you would need to prime and paint the new metal to prevent a recurrence of the rust.  If the current rust can be removed by sanding, grinding or wire brush, I would keep what you have and prime and paint.

 

[TrainChaser]

I recently watched a YouTube video on removing rust with white vinegar (About $3/gal). You could soak the plate in it in a piece of plastic or wading pool, if it would fit. Or, get a bath towel or something that holds moisture, lay it on the rusted side, and saturate it with white vinegar for a few hours, then check it. Scrape/brush off the rust, repeat if necessary.

I haven't tried it myself.

 

[BradKW]

Rust converters are a good solution for most any surface rust or cleanable scale. They convert rust (iron oxides) into a stable and protective layer of either ferric tannate or ferric phosphate, depending on which product used. I prefer the tannic acid based Corroseal for most things, but Ospho definitely has its uses as well...