I flew into BRU several times during the late 80's when living there (otherwise, I lived in the US and am a US citizen). Belgian customs never said a thing. There was no customs form to fill out. Several times, I checked in 2 large boxes, each weighing as much as 70 lbs. If you want to check if there is a difference in customs allowance between visiting Americans and temporary residents, you may ask the consulate. They may not know and place you on hold. I never checked their website (if any)