[NoBones]

While your plastic is in the workable stage you have about
30 seconds before it starts to form, just reheat the area again before it sets. In this time frame the reheat only takes a minute to make the plastic workable again.
Do 1 side first, that will help you on the other side for the 1/4 inch gap. When you are heating the plastic making the 90 degree bend a wood saw horse works fine.
See ya, Ken