Responding to feedback, I have added a version with NO BRIM. I originally added a brim just in case of curling due to the thin base and walls. It's probably not necessary but peace of mind for little extra time and very small effort in removing it afterwards.

There are numerous variations out there for this product. I wanted to print a simple but effective dump box and I thought instead of using magnets to hold it in place just use the existing screw that holds the chute in place.

NOTE: I unscrewed the original black screw from the lower mount of the dump chute. Then used one of the slightly longer silver headed screws - I think it was used in the packaging material from delivery. Leave it unscrewed a little for the chute to clip onto.
This design appears to be very thin in body thickness but I didn't see the point in printing one with 3mm or 4mm thick walls. It only holds lightweight filament. This is easy to remove for emptying and does not effect rolls mounted on the rear of the printer.

I'm sure other designs serve their intended purpose. This is a very straightforward design and I thought it might be useful to someone.
It might appear to be a remix of someone else's work and with the amount of these chutes out there it's quite possible. Apologies if this is the case.