Need help designing front and rear Cross Sections.

Starting my 4x8 build. My plan starts with a 5’ 6” overall width limit so I can fit my TD under my Deck for winter storage. This will keep the rain and snow off my TD when I’m not camping.
I read that keeping the body width at (or under) 4’ will allow me to use standard size Aluminum and Plywood. I’m planning on using ¾ ply sides, so that makes my trailer width 46 ½” (48-3/4-3/4=46 ½)
Now I need to know how long to make my trailer base. I have a shape,

How much trim? Mounting area? “Whatever is down there” will I need to mount the base of my curve to my trailer?

I read that keeping the body width at (or under) 4’ will allow me to use standard size Aluminum and Plywood. I’m planning on using ¾ ply sides, so that makes my trailer width 46 ½” (48-3/4-3/4=46 ½)
Now I need to know how long to make my trailer base. I have a shape,

How much trim? Mounting area? “Whatever is down there” will I need to mount the base of my curve to my trailer?
