One problem related to tank assembly has been reported for the 2003 Mazda B3000. The most recently reported issues are listed below.
I was driving into the mountains of nc from SC. Smelled smoke. Realized it was coming from in between truck cab and bed. It was very difficult to put out fire as it had started to melt the plastic bed liner and plastic gas tank. Fire was caused by a 2 foot by 2 foot piece of cardboard that had fallen down between bed and cab. It was resting on the gas tank and leaning to the side on top of the muffler. I assume it caught fire as we traveled slowly up the winding road. (hwy 276) there is no shield over the muffler. When the tank was replaced it was reported to me that the fire had melted the top of the fuel pump and had exposed a hole in the gas tank. I believe this a very serious problem that needs to be dealt with by Mazda.