You know, as someone who basically built your wedge shaped trailer (but not as extreme) - I have to say, making things square is a lot harder than you might think starting out as a novice. After seeing just how easily the plywood will bend- frustratingly while trying to install it, I think if I ever build again after this time I'll be adding rounded elements. plus, it adds strength while removing weight.
I honestly think maybe next time, i will look at a design more like This: /_D
My tow vehicle has a big problem with backdraft. you can see the results of it after driving down any dusty dirt road. the front 7/8 of the vehicle will be completely clean, leaving the back gate and rear covered in dust. Having the front of the trailer slightly slanted will hopefully allow that backdraft a place to 'smooth out' and flow down the back of the trailer.. possibly even improving fuel economy.