The 921 versions of the bulbs I linked to will fit fine into the inside fixtures and are only slightly less bright than stock. Certainly bright enough with the white ceiling reflecting the light around. LED trailer lights is a one man operation, as far as I can tell, and his stock comes and goes. Contact him and ask for the bulbs, he may bring them back into stock.
LED bulbs are everywhere, SUPER BRIGHT LEDS
, EBay, and Amazon are other places to look. The problem I always run into no matter where I look is bad website design, poor descriptions and the use of one image example for different types of bulbs.
LED lights are not just an Aframe question so check the the broader forum for other threads. You can also check the long threads on the PopUp Explorer Forum
for and almost endless discussion.