Have you tried a glue for PVC tubes? Clifton urethane adhesive, Sta-Bond, VynaBond, Aquaseal; any of these (or other similar urethane adhesive) should work.
Rough up the PVC, hit both sides with a solvent to strip off any remaining oil(acetone or MEK should work), and glue per product directions.
If you use something like Aquaseal (a urethane glue that has a liquid accelerator), you can cut it with something like 2:1 or 3:1 acc to glue which will allow it to soak into the velcro fabric backing a bit better. Then glue per directions using the aquaseal coat as a prepared surface.
You might also try adding biggish reinforcing patches, and riveting (or grommeting) the velcro on.