I would white coat the roof with Acrymax
Acrymax Technologies, Inc. - Flexible Solutiong in High-Perfomance Coating Systems! AND insulate the the space under the roof. Remember, heat travels by radiation, conduction & convection; so the best game plan addresses all three. WRC only really addresses radiant heat gain.
Perhaps a access hatch could be made in a closet ceiling to gain access.
I have metal low slope roofs on my 1880's Second Empire style house & it has made a bid difference.
I power washed the roof; put down the base coat (with roller). You then roll out a layer of fiberglass mesh which becomes embedded in the wet undercoat. Then you roll on the final reflective coat. I first did white roof coating in about 1984 (when I learned about it from the National Park Service), and did a top layer recoating last year.
I also tried EP Henry's & Ames Labs similar product, which are less expensive. That is because they have more liquid and less pigment. The roof I did with EP Henry lasted only about 4 years, Ames about 7. I have gone back to the Acrymax.
To maximize its efficiency, you have to keep it clean, so consider giving it a wash before hot weather.
PS: I have NO affiliation with any material supplier or manufacturer whatsoever. I am only interested in results.