My mate doesn't know the method used during the camp he was on but there is a little more information here...
http://paleoplanet69529.yuku.com/topic/34478/t/Tanning-Fish.html
... ETA: I will post a few recipies in the following days, can't do it right now.
Given the exellent information here, there is no need to repeat it. I'll just add the following from the book:
Unless being tanned immediatly the skins are preferrably to be put in the freezer rather than salting or drying. It helps make the skin softer in the end.
Scrape and take the scales off if it has not been done before. She use a scraper made from bottlecaps. If the scales are small they can be left for now because they will fall off during the tanning, but be aware that scales left on will cause discolouration.
Urine based tanning:
"The urine must come from a baby boy, who is only breastfed"
The author claims that no smell of urine can be detected if baby urine is used. The longer the skin is in the urine bath the softer the skin becomes. Half a day or more - over night.
1 litre baby urine ( ½litre adult + ½ litre water)
½ dl olive oil
1 teaspoon soft soap
put the skin in for 12-18 hrs, stir often and keep around 20 degrees C
wash several times in soft soaped water (1/10 soft soap/water).
take them out and let dry to a "dripping free" state.
refatten the skins (sorry for crappy english, can't really translate in real time) for 5-10 mins in no warmer than 25 C, in this solution.
½ litre water
1 dl olive (or raps) oil
2 egg yolks
1 tea spoon soft soap
Hang the skin to dry or put it with the outside towards a glass sheath for a shinier surface.
before it is totally dry begin with the softening. Fishskin is less elastic than mammals hides. Rub it between the hands both lengthwise and crosswise. It seems any means of working the skin can be used, pullingback and forth over the back of a chairLet it rest when the surface is dry so that the moist inside creep to the surfce and then workj it again. Do this until it is dry. If it dries to fast it can be remoisted with a spray of water. If this process is stopped to soon the skin will become hard again.
In the end the author use moistiuriser.
To make the skins smoother they can be slightly dampened and attached to a flat surface.