It all depends on what you're getting. If you get one of those $25 panels, those will probably take 2 -3 days to fully charge a battery.
If you decide to spend a little bit more and buy let's say a Coleman CL1200, that should keep your boat running on Dexter for a whole day and still keep your battery charged.
Besides, you are not going to be cranking the power all the way on your trolling motor anyway. Trolling with a 45lb thrust on a 9.5' boat at speed 1-2, your battery (a deep cycle marine battery) should be able to last a day.
If there are any outlets in that camp ground, you could also get a $40 Husky recharger, which charges the battery overnight.