note - at the best the prior method requires no measuring and marking.

but a big question. Why build these DEEP and stiff floor cross beams?? why lose all that precious inside space?? why potentially damage the truss intersection by rigid attachmt and screws. why be a walrus on the outside and a pipsqueak inside?

so replace all the floor beams w/ a thin laminated curved beam say 3/8 or 1/2 in deep by 1 1/2in wide with a small gusset type connection going in the littl space betw the diags. ( scalloping is the reverse of the direction desired(for space)) And tie or flex glue in place instead of screwing. {conceptually you'd be just grouping traditional ribs tight to each other(consider as one mass), then space, then group etc.)

YOu'd get much more space, more accessible space(no hang ups-easier to slide in baggage), more flexible floor(already lots of stiffness in the side trusses), and therefore less possible damage at the truss/beam location.

makes sense to me.

-mick