I WOULD STILL REINFORCE WITH METAL BRACING. RULE OF THUMB. IF IT CAN GET WET IT WILL. WATER IS THE BIGGEST ENEMY OF WOOD. SO SPEND A LITTLE EXTRA AND REINFORCE IT. IT IS STILL A LOT OF WEIGHT BUT THE LAST THING YOU WANT IS FOR THE WOOD TO DISTORT WHEN IT GETS WET. THE DESIGN LOOKS GOOD THOUGH. POST SOME PICS WHEN YOU GET IT DONE.
