I'm attempting my first trailer frame build and am concerned my design has a couple of weak spots but don't see a good solution. The intent is simply to enlarge cargo space with a 4' W, 3' D, 2' H cargo box that can carry camping supplies and the like. The overall length is just over 7' and the frame is 4' wide. It is also designed to carry a medium sized tongue box. The tongue consists of a single member extending the entire length of the trailer and two side rails to stiffen it. My concern is the joint where the side rails join the box frame. I've changed the original design to where i'm mitering a single length of tube to extend from the nose back to form the rail the axle spring will mount to. My thought is to plate the mitered joint on three sides with 1/4" plate (shown in illustration.) I also intend to put 14 gauge sheet as the floor in the trailer and the box will be built on top of it. For the box i'm using 1" X 1" .063 square tubing with the addition of 1" X 2" at corners and for the lid framing. the following images are the work in progress. i'm guessing the weight of the trailer around 450 lbs with a 1000 lb. payload max. any thoughts are appreciated..