Land of Sand
The Land of Sand is the light novel that the Other Brothers Elric episodes, and the Warehouse episode comes from.
In this light novel the brothers visit Xenotime, a town that was once a thriving gold mining town, and before that an agricultural town. However since then the gold has dried up and the land had been rendered unfertile.
Two imposters have been using the brothers names to work at Mugear's laboratory and try to make a philosopher's stone.
While the Other Brothers Elric episodes are based on this novel, it's not a 1:1 adaptation, so if you'd like to see more of the Tringham brothers, or just a bit of a different take on that story then reading this one is worth it.
The Warehouse 13 bonus story is also different from it's anime counter part and also a fun read.
It focuses on the boys of Team Mustang as they investigate the Warehouses at Eastern Command in the middle of the night for proof of the tale of Warehouse 13.
There's also some art that was made just for the light novel by Hiromu Arakawa.