You're not getting it... Build a UDS, you'll be nothing but sorry if you don't. The fire basket is so far away from the food, it's just like cooking in an offset. I can't find a decent 30 gallon build thread after a quick search, but I know they are here somewhere. Maybe someone who has build one will chime in.
Any high temp rated paint in a rattle can will work fine for the outside. Krylon BBQ black.
You keep rust out of the inside by seasoning it like a cast iron pan. Spray pam or the cheapest cooking spray you can find all over the inside, then do a "seasoning burn" to set the oil into the metal. No more rust.
Rescued 22.5" OTS. SJS Mini-WSM. HEB briqs (rebranded Royal Oak). Pecan/Hickory/Cherry/Apple/Peach woods.
2016 Fuji Absolute 2.0 LE (for burning off all the great BBQ)