What is the thickness of your fish paper? And how tight does it need to bend? I think you could use some kind of plastic sheet as replacement. It just needs to be abrasion resistant. I think fire resistance of insulatoros is overrated as once the cells start to burn ain’t nothing stopping it.
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Fish paper is not meant to be fire resistant. As you said it just needs to be abrasion resistant. It is not that thick, I have not measured it but I guess 0.2-0.4mm.
Fishpaper is meant to be more abrasion resistant than most plastics while not being abrasive itself. This is especially true when vibrating against other things could cause a rubbing action and wear through plastics.
Fishpaper is not meant to be fire retardant. It is simply a very good insulator that is free of any conductive particles, has very good abrasion resistance, can absorb small amounts of moisture and is foldable/easy to conform around electronics.
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Definitely going to be tight.
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Maybe to switch one or two p groups to the down where now is a lot of free space?
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I would have to get different nickel strips otherwise it’s gonna suck. I will need some of this space for the BMS and the wiring.
Why different nickel?
If you swap the last two 7p groups like this
You just need one connected soldered with 2x12awg wire to the other packs.
You still have enough space than for the bms.
Then it would look like that
I could put the cells not staggered like I have them now but I would need this type of nickel strip.
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Why? 
Sorry 
but I still don’t get it.
You don’t need to change anything in the nickle lay out.
Just one side of the 2s7p group has only one nickel stripe, plus you need to connect this pack with 2x 12awg to the other ones.
No need to change the layout of the cells to quadratic scheme.
So you mean put them like the drawing?
Yes why not? Just use some foam or neoprene to fill the gaps and you should be good to go. Why you think you should need to change the layout? The only advantage I can see in the quadratic lay out would be that you have a bit more air inbetween which gives more oportunity to cool down the cells. But I think that’s not really a big issue.
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I prefer to have a tightly packed battery. Less chance of something breaking or coming loose. I have enough space to make it like in the photo, even with fish paper between the p groups.
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Hey man that’s alot of money to burn, please use fishpaper, hot glue alone is not enough I don’t want to see this build up in flames.
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Who said I am not going to use fish paper? Edit: I see how you could get confused. I just asked if I could skip using it but in the end I have enough space to use fish paper and even if I did not I would rearrange the pack in order to use it.
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Progress
I kept my batteries warm to make sure I got the best out of them. 
Let me know if you see anything dangerous and/or bad practice. @Acido @pjotr47 @psychotiller @deckoz
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First thing: welds looks very clean. Good job
Do you gonna put your battery under your board? Or in a case on your board? If so watch out with those nickel strips. I think they can hit the other packs if you place it in a flexible enclosure 
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They will be placed as they are in a Trampa monster box. It will be a whole “brick” and all the p groups are held together with hot glue between them. There is a photo somewhere up in my thread that shows approximately how they will be placed in the box.
Beautiful spot welds! What welder do you have?
edit: The malectrics with a lipo battery
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Welds look really nice, make sure to test them every once and a while
Also I would put something like fish paper between the p packs
Or glue them together so they cant rub against each other
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Thanks. Technically it is two Lipo batteries. I tried with one at first but I could not get solid welds when testing nickel to nickel. Nickel to battery was fine but I am too anal to let these things pass. So I sacrificed another 6s 5000mAh battery to make 2 more 3s.
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