yes use L-brackets the dont add to too much weight for all there worth
and if the ends are fiberglass why not just glass it all its not very hard and that way you would have all the great performance of wood and the added strength of the fibergalss but it would still be able to give a little allowing for a smoother ride then a metal frame
the only problem with fiberglass is its kinda messy to work with and if it gets on a tool or something you might have to throw it away
and I second what andy said about the inner wheels