Stripped footstrap hole

[Floyd]

Helicoils are principally designed to replace lost threads in metal.Forces involved in putting one in place might damage the plastic but I`m not sure.It woul also mean using different screws.(ie machine screws rather than self tapping)
As daft as it sounds best solution for a really damaged thread might well be a simple wood screw rawl plug.(Of appropriate depth /diameter) You wuld have to be very careful drilling out to fit the plug.) Experiment on a bit of old plastic ???