Using an OTG setup with a flash drive for roms does not work with the LB Android APK. Parsing of roms gives a message saying that the SD card and internal storage have no roms to scan. If you try to manually add roms the LB browser cannot find the external storage.
I exported my romset from Windows version and put on a flash drive when I attempted this. The program loads fine on Firestick and it can scan internally saved roms just fine, but with the small space on these Amazon machines, the ideal way would be to parse games off of a flash drive. Unless I did something wrong with regard to how I installed LB's APK or exported my roms from W10, it appears that the program is limited to just using internal or SD storage. If anyone has any advice, I'd appreciate it, if not I think I just have to wait for an update to LB on Android. Either way, it is a marvelous program and I am super thankful for the devs. Proud to have donated for Big Box!
Sidenote...I installed LB APK onto the Firestick via Total Commander file manager app off of a USB flash drive.