Id start with rock salt or other 'sno-melter'
Start in the middle and then make an "X" across diagonally from each 'corner'. The danger with ice is that when it 'warms', it expands and the pressure developed may well cause spider cracks, especially along the flooring of the cockpit and the 'corners'. Once you get the X, etc. done and the ice is free on 'one edge' so it free to expand, then you can use heat to finish the job.