To do it right would be to take it off the back , if the top looks like that the bottom/sides will be just as bad.
Take it off , wire brush/sand it down clean all 4 sides, wash it good with a strong detergent and a through rinsing then dried and wipe down with non tack cloth with alcohol,or any surface prep material. Use a good primer,a good quality paint then paint several thin coats...
You will get overspray on the back side of the MH if you leave it on and try to do it...
Now that that is taken care of and drying you can do this ;
While its off now you have a clear shot of the receiver hitch, get a piece of cardboard and rattle can spray the hitch while deflecting any overspray with the piece of cardboard...