Extending HC-05 antenna outside Aluminium box

Hi, I am placing an Arduino Mega 2560 and a HC-05 Bluetooth module inside an Aluminium box, which will be potted (epoxy resin filled) and then installed inside a Stainless Steel box.

Obviously, being inside all this material, I do not expect the Bluetooth to work! I have seen some topics about adding an antenna, but they all talked about just using a single copper wire, etc. I would like this to have a professional-ish looking antenna, which will need to be mounted on the outside of the Stainless Steel box, and be somewhat waterproof.

I am looking for any advice regarding sourcing a good antenna, and how to go about adding it to the HC-05 (I believe I need to cut the link to the pre-existing antenna?)

Bluetooth uses the same wavelength as WiFi, so you should be able to get one of those standard WiFi antennas and use that. I imagine you just use the pre-existing antenna as a solder pad.

It's not that simple.
The OP seems to be potting the device and any antenna connections will not be accessible. The antenna connection needs to be extended with a length of 50 Ohm coax to the first and second enclosure.
And that begs the question as why all the trouble of potting the thing when the coax is likely to be an invitation for moisture to get to the board, anyway?

While potting inside the Alu case is partially for water-sealing, it is also to "strengthen" the internal components, and lock all the connections in place, as this will be mounted onto a truck. As long as the Stainless box remains mostly water-tight, then the Alu case doesn't matter so much.

So based on the comments, I should be able to solder some 50 Ohm Coax to the HC-05's existing antenna, run that out of the Alu case, then join it to an antenna on the Stainless case, correct?

Correct, but you HAVE to cut the trace where the antenna begins. Not having a clue as to what you have, you will have to determine where to cut.
I hope you thoroughly test all this before you begin to put it away permanently.

Yes, the goal will be to test everything before fully potting it.
Thanks for your help