I could not find any info on this unit would be a real pain and probably cause an arm and a leg if it is available.

There is a self sticking silver tape that is made to repair cracks in liners usually used on the back side but in this case you will have to use it on the front, Won't look pretty but should do the job. The glue is very sticky so once on you apply it you are not going to move it.

The glue backing is fairly thin, it is also be available at lumber yards where it is sold to seal ducting.

You will have to cut out the deformed plastic. Then you could build up layers of tape so it matches the outside profile of the liner. You could use other materials to build up the area under the hole but it should be hard otherwise if you hit your patch with something you will end up with another hole.Then put on a final layer that is half an inch to an inch bigger than the hole.

I would try a small peice of the tape on the styroform first just to be sure that the glue does not eat the styrofoam.

Hopefully someone else will jump in with a more elegant solution.
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I do not know what type of plastic the liner is made of so cannot suggest what type of epoxy could be used. It is essential that any type of glue/epoxy used is made for the plastic or it will not hold.