For anyone that watched this and still can’t get the access panel off, there are two more hidden screws besides the ones mentioned. After using a heat gun to peel out the gasket (thinking that was the reason mine wouldn’t come loose) I discovered them. They are located under the transmission mount and you can’t get to them (at least I couldn’t figure out how) without taking the mount off. This is a good video though and extremely helpful in removing the tank!
You probably already know by now but if you don't, the reason someone cut that hole just before the top engine hatch is to change the fuel sending unit. Some people would rather cut a hole in their bus than pull the fuel tank.