I have two Ehiem
External Eco Pro 2036 Filters, and they fit fine in each side of the cabinet. What is your filter model?
The internal dimensions of the cabinet are 12.5 inches deep X 27 inches high X 9.5 inches wide. The issue you have is with the width, as you have to allow about three quarters of an inch for the depth of the door when closing it, this would also apply to the depth too I guess. If you want to be 100% sure then email Juwel and double check with them. The main issue I have had is getting a tray the right size for the bottom of the cabinet, just in case of any initial leakage, it is fairly small hence most things are not suitable for the dimensions of the filter/cabinet. Based on your measurements of mm 333 x 210 x 300, it will depend on which measurement fits which dimension as to whether the filter will fit? The other option maybe to put it in the middle as there you do not have a door to contend with, or remove one of the doors, or put it at the side of the tank?
It is a lovely tank, yet to fit an external you will need to make some slight modifications in the lid to accommodate the pipework. I got mine second-hand for a steal off Gumtree, so this was already done for me.
What colour are you hoping to get? New or second-hand?
Can you
action this, as it will assist in helping you further.