This is a joint detail for two panels with wood edges, and held together with a glued and keyed joint. No more attachment should be needed. The pink is 2" thick foam insulation like available from most home stores. the wood edges would have to be milled to the thickness of the insulation.
Before gluing to show the panels and key block.
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After gluing panels together.
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With the added surface are provided by the key piece, and it's placement, the joint has sufficient glue area, and multi directional glue planes so it will hold up to forces trying to break it apart. Water ingress can only happen at the inside corner and outside corner. The inside corner could have a caulk bead ran along it. With a quarter round at the outside corner, bending the aluminum skin around, then overlapping it over the bottom skin water ingress can be eliminated. The wood could also be pretreated with pore filling epoxy resins to be waterproof in that corner. They just need to be compatible with the skin attachment glue.
An alternate corner for more strength against external impacts to it. This was designed for a hard sided popup so there are two wall sets. The one with the rounded outside corner is for the popup top. The aluminum sheet is bent with a 2" radius via a slip roll of sufficient length. the rest of the pieces are common off the shelf parts cut to size. The red blocks are plastic glides, and likely should have a bit of gap for easy sliding. The darker orange are SIP panels. The lighter orange is spray in foam to fill the voids. I think I was planning on using VHB tapes to glue the panels to the angle irons and outer corner. Any automotive body gluing technique could be used.
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You could make that outer corner in the above a bit stronger using hat channels to stiffen it up. The hat channels can easily be bent using a metal break.
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You may also wish to look at this thread for more ideas.
Travelling Cruisers The cruiser build in it uses an external frame with SIP panels.