The "easiest" launch we have is at a ramp that is steep enough to require a complete dunk of the trailer. The guy we bought our 16 from did us a "favor" by drilling 3/8" holes in the bottom of the molded plastic car top type trailer box for drainage. Now we have to make sure there is nothing in it that can't get wet before we launch and must wait 'til it drains completely to throw stuff back in.

If building new I'd opt for a top entry only box and install a few removable drain plugs.

Bearing buddies, for periodic greasing, work great along with the yearly removal and inspection.