3 cheers for your hard work!! We had to replace the floor in our original trailer. The seller had it outside for several years and it was never sealed. Thus, at 3 yo it was rotting out!!
Your trailer is going to look like a gem when you're done. It ISN't overkill to treat the metal and then use Rustoleum.
If you have cable or Satellite, you NEED to watch "American Restoration" on the history channel. American Restoration — History.com TV Episodes, Schedule, & Video
Some of the machines and toys they have restored are BEYOND GONE when somebody brings them in!
Have you tried to buy Rustoleum lately? The only place I can buy it without some clerk lecturing me about how VOC's is at a regional farm supply store, "Rural King." FIND YOUR STORE!! I think white would look nice, but they sell the same colors in a small spray paint size, and I highly recommend you buy one and look at your color before you buy the gallons. I bought 5 gallons to cover the outside only of my 4-horse slant trailer, and I needed slightly more than 4 to cover. If you buy 3, you'll have PLENTY, and probably will be able to cover inside and out. Go with a standard Rustoleum color, so you'll be able to buy more in the future.
My trailer went from rusty Midnight Blue to bright Royal Blue.
I thoroughly enjoy my paint job every day!!