I concur...and if you've not used a heat gun before, start slowwwly on the lowest setting. They can get away from you. I also recommend a pair of leather work gloves because you're gonna want to push that insert around while it's hot. The hair dryer might work...my daughter's is about 2500 watts (based on last months electric bill.)
It appears that your boat may be hanging in slings? If you have a trailer, it might make a more stable, accessible platform for the chore. Like painting, good prep is 90% of the outcome.
I'm guessing the 'dent' may have to become a war-wound unless it's just pushed under in the photo...hard to tell.
Cliff