I will be building my own trailer instead of modifying an existing design.

Here is where I am having trouble. I am sketching my design out on a scale of 1 inch equals 1 foot. I have designed it to a tire diameter of approx 30 inches. When I do that I am guessing that I will have a 24 inch clearance from the ground to the bottom of the camper, and with that I have approx. 5 inches from the top of the axle to the bottom of the frame. Does this sound right? I am not sure about the spring and shackles what that will give me or how much travel I will have when they are in place. I want the springs to be on top of the axle, I think that would give me the most ground clearance. I will be building a 5x10x5 unit. ( That is 5 feet wide, 5 feet high and 10 feet long. ) With these measurements I get a hatch opening of 7 feet that is letting the hatch open to the level of the top. Then if I add a rack on top that will let the canoe on top remain on top and still use the hatch. This is for an off road design. I like to prospect and the like. Do I sound like I have learned a thing or two reading this forum?

About asking for help that is? Thanks!