B&C Double 15 BR

I'm a full time professional sound engineer working on TV and live events. I work on some pretty large events but I also do some smaller shows, with my own small PA, for a few hundred people.

I am quite knowledgable in general audio theory, and in system design and deployment for large venues, but not so much with cabinet designs so I'm looking for some help!

I have 4 B&C 15TBX100 drivers and would like to build a pair of 2x15 reflex boxes. I would like to keep it simple as I'm not much of a wood worker haha.

I've messed around in WinISD and keep coming up with designs that look suitable in terms of freq response, excursion, and port velocity, but they all seem to require very long ports. I've been told that if the port is a slot design utilising one of the boxes walls it can be shorter? Is there a formula for this?

I guess I'm just looking for some guidance on designing a simple to build BR box for my drivers. I think I'd like to tune the box somewhere around 35-38Hz but I'm open to suggestions.

Current system is Nexo PS15's and RS15's. I'd like the new subs to be useable on their own as well as in combination with the Nexo subs.

I have a rack of Powersoft T-series amps to run it all. The subs will be on a T-904 in bridge mode so 2x 3600W @ 4 ohms :)

Thanks in advance for any help!

25mm ply seems a bit excessive.  I've built plenty of bass cabinets out of 15mm ply, just needs a bit more bracing.