I've built a number of simple craft-box or foamcore box cameras, using as a common support a piece of wood with tripod nut and several brass hooks on the sides to attached bungee cords. The wooden base gets attached to the tripod head and I can carry several box cameras in my backpack.

Alternatively, I've also built foamcore box cameras with a storage compartment in the back for exposed and unexposed sheets, changed out using a changing bag. For these types of cameras I build the bottom of the foamcore box onto a dedicated piece of wood, with tripod nut built in. Then, all I need is a large changing bag carried in a small daypack, plus light meter, notebook and tripod.