Here's a couple more of the tatty old girl....
The blisters are indeed being removed from the Mk 5s due, as my namesake says, to the aerodynamic issues of turbulent airflow over the elevators.
As for the neoprene covering, Simon is quite correct as to the whys and wherefores of the stuff. Worth noting that due to the direction of the prop rotation the covering extends all the way up the fuselage on the starboard side but not on the port (first picture above).