Flat panel or wafer style LEDs with T-10 base installed in 7$ single or 9$ double fixture (Bargman) from Amazon Prime have worked well for me in replacing trailer interior lights
. At one time, I soldered T-10 pigtails to BA15 bases for the old Illuminaire fixtures in the Burro
but those fixtures are gone and hardly missed. I never cared much for the MR socket and bulb used in track lighting
but can see why an MR base would be useful for adaptation of that 12V system to LED illumination. At 6 bucks the bulb, it wouldn't be my "economy" choice for LED lighting
unless needed to adapt factory track and sockets.