Great post, Andy, clear and concise.

It is difficult to do damage to a Chainglider, so cutting -- a bread knife is good for this -- or rasping away a small indent with a wood file, needn't be terminal if one takes care to remove only a small bit between pauses to offer up the Chainglider to the frame to check progress.

I like your heating and reshaping innovation very much.

Lots on here about Chaingliders but I could not find a thread on fitting them to Thorn bikes, specifically the Raven Tour.

The problems:
There are two problems with fitting a CG to a Raven Tour:
1. If a Thorn alloy chainwheel is still fitted it will need to be replaced as it is 5mm wide and the CG spec says the max chainwheel width is 3mm.
2. The seat stays on Thorn bikes are closer to the chain than on some other bikes.  This is compounded by the fact that over the years Rohloff have increased their recommended chainline and Thorn bike frames were designed at the time of the narrower chainline.

Different Rohloff sprocket carriers require different chainlines:
- threaded (chainline 54mm)
- splined (chainline 57mm)
- threaded converted to splined with the thinner adaptor (chainline 55mm)
A narrower chainline gives more clearance between the chain and stay so a Rohloff hub with the earlier threaded sprocket carrier is best.

Solutions
1. The chainring - simply replace with a thinner chainring.
I used a 4mm thick Shimano STYX 38T alloy ring with Narrow / Wide teeth for no better reason than I have had one on another bike for 7500 miles with a CG.  Being 1mm wider than ideal, however, it does make a sound like a squarking chicken when wet but I know this will go with time as the CG wears in (the chainwheel on the other bike did not not wear, it was the CG that wore down to size).

2. On my Raven Tour (threaded sprocket carrier and 537L frame) the closeness of the chain to the stay meant that the rear section of the CG was being pushed slightly inwards.   Long term this could result in paint damage to the stay and the risk of the CG rubbing on the soft but expensive alloy hub.
My solution was threefold:
1.  File off about 1mm from the top corner of the rear section of the CG where it touched the stay.
2.  Heat the rear section of the CG in the area where it touched the stay with a hot air gun and push the now flexible material inwards maybe 2mm with a rounded piece of wood.  The plastic appears to be ABS so becomes hard again once cooled.  The geometry of the rear section of the CG allows this inward bulge to clear the chain.

These tweaks gave about a 1mm gap between the stay and the rear part of the CG.
The final detail was to stick a piece of clear plastic Gorilla tape on the stay to protect the paint, which reduced the gap slightly.

Different combinations of Thorn bikes / frame sizes / rohloff sprocket carriers may need different solutions, for example cutting away part of the rear section of the CG so it clears the stay.

38T, 104BCD, 5mm thick so no good for chainglider.
Not been flipped, a few light scratches on outer side
£20 plus postage (new £50)
Please PM
Am in UK

One conclusion I derive from your description is that you have also proven a useful intangible, that your stated intention of keeping it as simple as possible is eminently feasible.

Pity that you won't be able to fit a Chainglider to make maintenance even simpler/less frequent.

After 70 kms on the bike I modified for the nature reserve I think I might be able to get away with fitting a Nexus 8-speed Premium hub (and Chainglider) when I go electric on one of my own bikes. I always ease off when changing a hub gear, and I noticed that power from the motor stopped momentarily when changing gear with the 5-speed (the Bafang motor is set up with a sensor that detects pedalling motion, as well as a wheel sensor that limits top speed). The 5-speed makes sense on the nature reserve bike, as the users won't necessarily ease off when changing gear like I do.

My long experience with Sturmey-Archer gears suggests that most problems that involve damage to the internal bits of hub gears are caused either by incorrect cable adjustment (not a problem with a Rohloff) or by not easing off when changing gear.

I don't use the electrical assistance and its controllers to maintain bike speed.

During my test rides I wasn't bothered about economising the battery. The assistance meant that I could accelerate faster with much less effort, go up hills significantly faster, and maintain maximum level speed of about 25 km/h with much less effort than unassisted. On the one moderately hilly trip I timed I took about 30 minutes instead of the 40 minutes it usually takes me without assistance, but I got less exercise. This time saving would have been useful about 20 years ago when I was commuting 22 kms each way, but not so much nowadays as very few of my rides are time-critical since I retired.

If the trike dealer used the Hubbub adapter, that is what I have on my bike that I showed the photo of in a previous post.
https://www.sjscycles.co.uk/gear-spares/hubbub-drop-bar-adaptor-mount-for-rohloff-63-mm/

That adapter sticks inside the end of the handlebar and gives me a place to put my Rohloff shifter.  The Rohloff can slide on either way, little fingers or big fingers.  The key point is the outside diameter of the tubing that the Rohloff shifter slides onto is the old mountain bike handlebar diameter, I think it is 22.2mm, but I could have that wrong.

If that adapter is what you use, you have to tighten it really good.  I have read that some people did not crank down on it when they installed it, and the torque from shifting loosened it up over time.  So, I cranked mine down really tight and it has been trouble free for the past 12 years.

I am quite happy with the external shift mechanism.  My bike frame came with cable guides for that version, so that is what I bought.  To remove the wheel, you unthread a thumb screw and remove the part that the cables are attached to slides right off.  If you get the external gear version, you should be careful when the wheel is removed that you do not move the shifter.  OR, the smart way to do it is put it in gear 1 or gear 14 before you remove the wheel, then make sure that the shifter is set in that gear when you replace the wheel.  I usually forget to do that, so sometimes I have to spend a couple minutes getting it right.