Well done. I'm glad you have got this far with the idea as it's an idea I've considered too, I think it has a lot going for it. Especially for working with basic sewing-machines in small spaces, but also as an elegant sail solution in its own right. 

However, my experience making my own sail makes me wonder if using the pre-made Keder is a little over-engineered.

I sewed a very loose bolt-rope into the top of my top panel where the sail slides into the yard and it seems plenty strong enough, my seams are also glued with a very tenacious basting tape. You don't have to sew a very tight bolt-rope edge as in the luff of a traditional sail, as long as the rope fits into the groove. I think routing grooves into wooden battens made from two halves is no big deal, easy with a router and appropriate bit but also possible with just a skilsaw, the groove doesn't have to be perfectly round, nobody can see it! 

It may be also possible and elegant to use the leech ends of the bolt-ropes for the panel holding and sheet fittings. 

Göran, here is another comment: I have to be honest and admit, what made me lean towards making the sail panels removable was - as an amateur first-time sailmaker - fear of managing so much cloth at the sewing machine when sewing all the panels together. The ability to remove or replace panels easily was really just a rationalisation (though later I did actually do that.) I suspect James G. will admit the same. I think Arne is right in saying you probably won't ever need to replace a panel, and on the matter of sewing all the panels together, maybe he can re-assure you about that.

On the other hand, if removable panels really is your objective, and you decide to save a little weight by using aluminium battens - there is another way you could consider, if you have not already thought of it - that is, the "horizontal hinge" system devised by Roger T and successfully used on Mingming ll. Roger built a very robust sail on his dining room table, with the lower four panels removable from aluminum tube battens. The method he used also provided the camber. 

Roger described it as being "like a piano hinge".

You can see on this link https://www.youtube.com/watch?v=E-IbUt-CTRQ how Roger made his wooden boom and yard, and attached his removable panels to aluminium tube battens. A little more sewing - but probably less work and a little lighter than the double-grooved wooden battens. (And welding a "luff groove" onto both sides of a set of aluminium battens just isn't going to happen!)

Roger's hinged panels have been well tested; another idea for you to consider.

PS My wooden battens do bend slightly. I have not had one break, but I would hesitate to make mine any thinner. Mine are 2 x 18 x 28 = 36mm x 28mm and the sail area is about 16 sq m.

PPS the junk rig is not simple to start with - but it sure is good and easy to handle.

Welcome aboard, Göran!
It gladdens me to see that someone is fitting an aux. rig to a motor-snipa. I have recently tried to lure an owner of a 20’ snipa (‘snekke’ in Norwegian) to add a little JR to it. As can be seen, the rig clears the windscreen and cockpit tent easily. I have positioned the mast a bit further forward than you as I suspect it would otherwise lead to some unwanted weather helm. Luckily there is room for shifting the sail a bit this or that way on the mast, to correct balance..

Rudder.
The rudder of your snipa looks better than most, so may work as it is. In case it feels sloppy with the engine stopped, it can be improved by simply adding an endplate to the bottom of it, and even a similar ‘anti-ventilation plate’ right below the water surface.
The miniature rudder of the Polar 20 snekke, shown below, surely will need and endplate on it.

Batten material.
The best natural batten material is no doubt bamboo, with its tube structure. However, since it isn’t easily available in Scandinavia, I now go for thin-walled aluminium tubes (‘Norway bamboo’). On your small rig for that snipa, I am sure you get away with wood, but if you are to make a bigger rig, say between 30 and 60sqm, I don’t think wooden battens are good.

Those tracks in the battens.
I have seen others using variations of the keder theme for battens. Their arguments were partly that it let them replace damaged panels, and partly that it was simpler. Personally, I only see the point in quick replacing of panels in case one is making an experimental avant-garde rig. Yours appears to be fairly standard, so it would be a lot quicker to sew the whole sail together, and use batten pockets as well.

Boom and yard.
For the boom and yard, I in any case suggest that you avoid using tracks, but rather add hoops at the head and foot of the sail, and then tie the sail on. This lets you adjust  the position of everything, like the halyard’s slingpoint (yard) and topping lifts and lazyjacks etc. on the boom. The recent photo of the JR of my IF clearly shows how things have been assembled.

Good luck!
Arne

(Full size diagram in Arne's sketches, section 4)

A report on my experiences so far.

Making the battens as proposed was straightforward. But the keder channels hade to be carefully cleaned from excess epoxy before it had cured. I also reamed the channels afterwards using a 10mm drill. (The C.I.Fall company of Eskilstuna Sweden makes a long-hole drill which can be lengthened in 40 cm sections.)

The picture shows a small prototype section with a 6mm line as filler. I realized that if one uses a single line for both channels of a batten the line forms a loop at the aft end of the batten to be used for fastening sheet blocks. 

Camber was built into each panel by cutting the sheets to the intended curved shape before attaching the lining. When inserted into the straight keder channels of the battens the panels will have the camber intended.

Now, when trying to assemble all this into a sail I immediately realized that the sail was quite heavy. The sail area is about 12 sqm, the sailcloth weights 8 kg, and - the battens, made from Swedish pine, weigh totally 16 kg! This makes a sail of 12 sqm area weighing 24 kg. I know that junk rigs are heavier than  other but...

i have halted the project now for a while to figure out how to proceed. Of course I can  use both a lighter sailcloth and lighter woods. Spruce is lighter that pine but difficult to obtain in knot-free lengths. 

i would appreciate any comments and suggestions. 

Keder, see https://www.jjcarter.com/keder2/what-is-keder is of common use for attaching sails to masts and profiles. I am making a JR for my small swedish open "snipa" (see my profile). The intended sail is a about 11.5 sqm, see "Rigg.pdf".

The idea is to fasten the panels to battens, boom and yard using keder, see "Lattor.pdf". The battens will be made from two halves of 22 x 45 mm wood (pine) where a 12 mm channel is routed. A 12 x 10 mm GPR tube is glued in this channel. After gluing the two halves together, 2mm saw is used to cut the groove for the keder. All this is simply made using a home shop router and a table saw.

A prototype panel is shown in the pictures attached.I have not yet found a solution to how to fasten the leech line to the batten ends. I will also make a practical test for the strength of the keder.

I welcome all comments and suggestions to improvements of this suggested method of making a sail with separate panels. Should i go on?