Trailer Project

[Hory]

I plan on redoing an older Spartan boat trailer for my 14 foot river boat. It currently is a tilt/lock trailer and I'll be making it a once piece rig. The trailer will be getting new 13inch wheels, a new axle, new bunks and carpet, lighted guide posts, LED light kit, new step-on fenders, and new main steel from the coupler back to where the main frame is. I also plan to weld the shackles holding the leaf springs directly to the trailer versus having U-bolts holding the shackles to the frame. The only remaining piece of the original rig will be the main frame with the rounded bends directly under the boat...(and this is where my questions come into play) I would like to paint this part black seeing as all the new stuff will be black too when finished. What steps would you take to ensure that the painting looks like a clean finished product? How would you go about sanding it(if necessary)? What kind of paint would you use and how would you apply it? (I really don't want a real glossy black, yet I want it to look semi-professional and not just flat black) If it matters, the framing piece I will be keeping is currently the original white color. Thanks for the help!