Are your seat runners free of rust and the seat capable of moving front to back? The Europa seats are secured with four bolts through the seat runners and fiberglass floor pan and held by washers and nuts under the bottom. You can access the front two bolts by moving the seat all the way back. For the back two bolts, move the seat all the way forwards.
If the runners are completely rusted solid which is pretty likely if water got into the cabin for any length of time you may have to get creative.