Impart on Me Thy Wisdom: A Newbie's Cry for Help

Howdy folks. I'm about to take on the task of building a new camper for my truck- no, it isn't a teardrop, but hopefully you'll appreciate it and offer guidance despite my blasphemy. I'm excited about the design and a foamie construction seems the most appropriate in terms of weight savings (my truck is weak). I'm really grateful for the huge supply of information here.
This is the Om Shanty's imgur album:
http://imgur.com/a/f5noc
Some questions to start:
I'm considering framing this in 1 x 4 Cedar, doing a PMF skin on the exterior and 1/8 plywood for the inside. Cedar is light, but I don't know how structurally sound it would be for this design. I'm really in the dark on this subject and I don't want to screw it up, basically. What would be the lightest material I could use and still have a structure capable of handling the stresses of traveling down the highway at 70mph?
The 4ft long cab-over is another question mark. Can I make it sound enough to handle two adults sitting on it? Again, I'm just making educated guesses here on what would work.
Any advice, input, inspiration is more than welcome!
Cheers.
This is the Om Shanty's imgur album:
http://imgur.com/a/f5noc
Some questions to start:
I'm considering framing this in 1 x 4 Cedar, doing a PMF skin on the exterior and 1/8 plywood for the inside. Cedar is light, but I don't know how structurally sound it would be for this design. I'm really in the dark on this subject and I don't want to screw it up, basically. What would be the lightest material I could use and still have a structure capable of handling the stresses of traveling down the highway at 70mph?
The 4ft long cab-over is another question mark. Can I make it sound enough to handle two adults sitting on it? Again, I'm just making educated guesses here on what would work.
Any advice, input, inspiration is more than welcome!
Cheers.