It could possibly have been the RV SunShade folks. They have several mobile installers around the country with some that travel around to different resorts and RV shows, etc. and can custom make those snap-on covers and sometimes can measure and install them the same day.
Here's their main website:
RV Sunshade Company
Here's one of their installers out of San Diego, for instance, Bob and Mary Jones:
RV SunShades Bob and Mary Jones
Here's a list of all their distributors/installers:
RV SunShade distributors
They also make the "invisible covers" but will have the snap-on type also.