I've never had to do it, but a friend painted his trailerboat bottom as follows:
Buy a set of two jack stands, position them on one side and screw the poppets up until that side is lifted up off the trailer rollers. Paint that side, allow to dry overnight and reposition the stands to paint the pad areas. Then repeat the same on the opposite side. If applicable, you may have to support the keel with blocks as well.
True Blue . . .
sold the Nauticat