Can't help with the panniers, but I did pick up something from another thread.
This is a quote from a thread on the IHPVA.org.
I use ordinary sprinkler tubing...the black plastic
pipe that sells for around 5 dollars or so for 50 foot
coil. Makes many pieces and is MY PRICE CHEAP!!!
Use a sharp knife to cut it nice and square and then
while holding the inside of the coil down, hold it
over a kitchen stove about 4 to 6 inches above a hot
burner to heat it. I then over bend it slightly in the
opposite direction from the way it came on the roll
when it softens up from the heat slightly and play
with it until it is almost perfectly straight. Main
thing is to approach the heat source slowly till the
'sweet spot' is found that has the right temperature
to soften but not scorch the tubing. I usually have
cut it about a foot longer than I want, this way I can
cut off the ends where my fingers tended to over bend
or mash it or whatever distortion I get near the ends
from handling. At about 5 - 10 cents a foot, cheap
insurance against excessive waste.
Grind down a big enough bolt or other spare piece of
round metal to a cone on the end and heat is up with a
burner/torch/stove and keep trying it till it is just
hot enough to flare the end. You really only have to
'cone' it down to the inside diameter of the tubing..
It is a waste of grind stone to make it into a spear
unless you need a spear for some other reason. Again
if you over heat it, it will make a mess of the end as
it is too hot and melts the plastic instead of
softening it. Make it smooth as possible and kinda
twist it in to assist the softened plastic to slide.
FIRST, Cut off short pieces (3-4 inches) and learn the
fine art of flaring...otherwise you may waste a whole
roll of tubing and still have bad flares.
Works for me.
I believe it softens around 250F to 280F degrees ...
not sure what exactly, so high heat...such as
reddening the metal would liquify it real quick since
that is over 1100F.
OH, wear good leather gloves with cotton liners. as
the plastic gets kinda warm. At least leather in palms
and finger grip side. Can be those cheapie gray cotton
knuckle side half leather gloves that all hardware
store sell. I like to wear a jersey glove inside if
possilbe when dealing with heat so I have time to exit
gloves if I get the leather toooooo hot.
This is from an 'experienced' chain tuber that wasted
about 20 feet the first time. Only sucessfully made
four that I needed for the Rhoades car.