I can't tell you how to build it based on what you asked but I can give you
some things to think about that normal boat trailer builder's ( let's
qualify normal to factory made runabout powerboats) may not think about that
may or may not effect your boat. Since it is only 300# one might assume
that is it lightly built. The "normal" trailer would actually use the boats
own stringer system to stiffen things up. Your boat may not have that
strength being so light. So you will have to give some consideration to
having a trailer that is stiff enough without any help from the boat. Also,
again assuming that your boat is not particularly strong ( being 300#, 19'
lg and designed to row in calm water) it may be somewhat delicate and would
need some type of cradle to support it over most of it's length. Anyway,
these are the things I would think about if it were me.
--
Ron White
Boat building web address is
www.concentric.net/~knotreel