I fixed a hole about the size of a dime on my sled.
Go to Walmart or any automotive store and get “plastic bumper” repair kit. Generally a 2-part expoxy mix.
Read directions carefully and thoroughly, as temperature is critical for the epoxy setting up correctly.
I placed a light layer over the hole on the outside. Then placed a piece of masking tape to “hold it” in place and help keep the expoxy in the hole. I placed probably a 1/8″ layer, about 2″ diameter over the dime-sized hole. You don’t want to “glob” it on.
Then on the “inside” of the sled, I placed another layer, same size.
You shouldn’t have to cover the inside sled layer with any tape. The gravity of the epoxy will fill the hole nice and smooth with the tape on the outside.
Make sense?
Also, black automotive spray paint will hold very well to this epoxy, so if you do it smooth, you won’t see it.
As for fixing a hole that big, I would cut a piece of card-board that is the same thickness, to the same dimensions of the hole. Place it in the hole and epoxy both sides, like I stated above. That cardboard will get sealed within the expoxy and hold well. If you have a 2-3″ hole, I would spread the epoxy atleast 2″ all the way around the hole to make a nice “layer”.