Here is my home built trailer. I have just over $600 in the material. 48" x 40" ply box on an Al trailer. I have 3 water proof box that are a good fit. It's kind of crude but good for the cost.
I have not weighed them...but the axle is well behind center so sway should not be a problem. I will load front heavy which will aid in tracking. I put a small spoiler on the back which will help with lift. I'll report on ride after I try it out tomorrow. I have much experience building trailers.
Might I suggest putting a rounded piece of light sheet steel or plastic across the nose and closing the sides in to aid in aerodynamics. That flat face, even though you angled the body some, is going to dig into the air.
I have a suggestion. Take the small leaf spring off. I did on my trailer and it tows much nicer without bou cing around. That trailer is rated for much more than you will ever load in it. It is very easy to remove the leaf. You will thank me.