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I think your question is a bit unclear. Why can't you fit the double rod? Are you carving the neck super thin? Have you considered routing a slot in the underside of the fretboard? Or you could just do a one way rod. With a super thin neck you shouldn't have to worry about it not bowing forward enough.

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You could switch to gluing in frets. I slot a touch wider than the standard and use Fish glue. The frets tap home very easily and then I simply clamp a caul to the frets until the glue is dry. They hold very firm providing that you don't go too wide on the slot.
It causes much less of a backbow because I've used it to fret off the Neck and even on a thin board I get very little bow. If I fret without glue, using the normal kerf, the backbow can be pretty severe. Stands to reason that gluing them in is putting very little pressure on the Neck.

Your sequence sounds good. I'd look at variations in fret tangs or fret slots. Fret tangs vary significantly, even when manufacturers say they don't. Pay attention to the force it takes to drive them in. I like to have hand saws that cut a variety of kerfs so I can fine tune the slots if I need to. Make your own fret saws out of band saw blades, and it won't cost much.

Put some tension on the rod before final levelling of the board so that you are removing a little from the mid area
That gives you some adjustment scope

This is one of those cases where it helps to radius the fretboard last.

In the PRS factory, they mount the neck into a jig, flex it back a hair, level the fret plane, then install the truss rod and glue the fretboard onto the tensioned flat surface, that way they have relief built into the neck shaft, and don't have to plane the fretboard. They radius their fretboard, then relax the neck out of the tensioner jig. I'd imagine this would also work with a pre-radiused board.

What I would do in my shop is I would glue the fretboard on and shape the back of the neck, then tighten the truss rod a hair , level the fret plane flat, then radius, also so that I would have relief built into the relaxed neck.

That is, unless I were to come up with a similar neck tensioner such as PRS uses, although theirs is designed to work with oversized blanks and their CNC machinery.

I use double truss rods and rarely have to be concerned with that whole thing though.

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Old growth, shmold growth!

use wider slots; fret fingerboard first, then glue it down

If your fretwire is a constant then the only thing that changes are the individual pieces of wood and/or humidity.
I use the Veritas handsaw or a thin kerf Bandsaw, if I'm using the Bandsaw to slot. I can't help you with the table saw blade information.

I ordered a fret saw to cut wider slots just for gluing frets in. I'll see if I can find the source.

EDIT: I found the receipt - Thurston Manufacturing Company. The one I got is an 0.035" kerf part # I301-5 with 5/8" arbor hole. They will make pretty much whatever you want.

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Steve Smith
"Music is what feelings sound like"

The slot width should change depending on the fretboard wood. For instance....022" grooves for maple and .023" for ebony will produce a tiny backbow, which straightens out with string tension. To avoid the backbow .001 or .002 could be added to the slot width but then the seat of each fret would be in question and glue would be advisable.

I occasionally measure tang thickness. Not often but I always use the same wire. So far I've never detected any variance from several orders. It's Dan Erlewine's favorite from StewMac.

Note that a V-neck can feel quite a bit thinner than a D-neck even if the thickness is the same at the apex of the curve. I make these two shapes with the cnc keeping every other aspect of the neck identical. The feel is considerably different.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

If a fretboard is really tight I use this to open the slots: http://www.stewmac.com/shop/Tools/Speci ... r_Bit.html

Works great with stainless steel frets with large tangs as well.

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Old growth, shmold growth!

With a single action truss rod:
Whether you fret before or after installing the fingerboard, a good practice is to use a curved caul to clamp against the fingerboard. The one I use has about 0.035" of lengthwise curvature, forcing the neck into a forward bow.
This is especially helpful with maple necks, which tend to back-bow from the moisture in the glue.
Another trick to lessen fret compression is to file the barbs off one side of the tang. I do it routinely on the fretboard tongue of acoustic flat tops. If I need to glue frets, I generally apply medium viscosity CA to the tang before installing them.

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John