To Sheath or Not, That is the Question

Sheathing adds tons of strength and rigidity to a structure, but also weighs a significant amount, something I couldn't justify if I was to stay around 2000 pounds for the "dry" weight of the finished product. Being a spreadsheet guru, I built a spreadsheet that would allow me to estimate materials

My fellow green innovator, James, helping to finalize the house wrap.

and the total weight they would contribute. Also interested  more in building something that met my specific needs and not too worried about anyone else at the lumber yard thinking I am off my rocker, I took a few trips to both Dunn Lumber, our local lumber yard, and Home Depot to use our home scale and weigh myself while holding lumber. I then subtracted my body weight to get the actual weight of materials.

You would be amazed at how much 2x2's, 2x3's, 1/4" ply, and 1/2" ply vary in weight, and how much they vary compared with "standard" weights one would find online. I likely saved a few hundred pounds by hand selecting the materials I used versus ordering them in bulk. I also took the time to hand select the 2x2's and open bundles to find those that were true and not warped. 2x2's in particular can vary in weight by up to 2 or 3 pounds and many are warped and not appropriate for framing.

To gain the most rigidity possible while reducing weight and giving the interior a log cabin like feel, I opted to flip the traditional framing process on its head and use the interior walls as sheathing. The walls then came together in this order.

Interior - 1/2" or 1/4" ply walls - 2x2 or 2x3 frame - 1 1/2" EPS insulation - Tyvek - Cedar siding

Since 1/2" ply was used on the front end and the roof fully connected to the walls, everything stayed plenty rigid. Near the aft end of the trailer, and where the pop-top did not provide a connection point
between walls, I had to use metal straps (salvaged from a nearby home construction site) to provide greater rigidity.

Steaming the front rad

For the from and rear "radius" and the top, I used moisture resistant underlayment in either birch or a sustainably produced eucalyptus 1/4" inch ply on both the inside and outside. This same process was used for the roof of the pop-top and did require some steaming and then bending to get the right shape without breaking the outer ply.

Sheathing on the interior, metal strapping for strength when using 1/4" ply instead of 1/2", and the original pop-top design.