We have started the build Irene and I have decided on a 5x8 so there is plenty of wiggle room. We are calling it the "Minnie Me" because we will paint it like our larger 5th wheel. Here are some pics....
Since we went with the 5 foot wide I had to build out around the wheel wells which took me some time. But got it figured out after some trial and error. I will have to cut the sides as well to fit. I also dadoed the edge of my 2x2 supports to allow me to rest the sides on it and screw them into the deck. Got about 20 hours into it so far, and have set a goal to be finished by the end of march, we will see......