Your current design employs passive tags. Those rfid tags are lit up by the scanner, and thus must be in very close proximity. There's nothing (that i know of)

Your current design employs passive tags. Those rfid tags are lit up by the scanner, and thus must be in very close proximity. There's nothing (that i know of) that will report its data passively over that distance. Alternatives could be Bluetooth beacons or something bespoke, but that will require powering the tags... increasing cost and complexity of operation. Edit: you can use computer vision approaches (like qr codes) if you have line of sight to each box. But that's not guaranteed if I interpret your problem correctly) Edit 2: if you do use RFID but position the reader near the trunk opening and scan each box as it enters the trunk, you can keep a running total of the weight added to the car. That might strike the best cost/effort/result balance given these constraints...