your concept for the double axle is excellent. I designed one similar many years ago for a company I worked for. We needed one that was easy to back up. from the configuration I would say this one is the same. it is clear you have some good understanding of the dynamics of a trailer. You will find that it is easy to handle and can balance it to provide a tongue weight so it can be towed by a small light weight truck. very good design. Keep up the good work and keep the designs coming......Grampa