For the bonding, you don't need to actually put the liners into the
tube, just into a short enough length where you can get it more
easily. If you can take a piece of pipe the same inside diameter, and
cut it in half, then you could possibly use those halves a molds.
Crack it open, lay in the liner, but the joints with whatever (I'd
maybe try to scarf them and glue with epoxy) aand then put the other
half on, clamp it shut and put in the bladder in the inside to push
out.
The scarf could be 3/4" long, or possbily longer if you can make it
work. Or if the liners are already in tube form, just a short section
of the outside needs to be supporting the joint when you butt them and
glue them together.
John