IDK, but the sissybar on my 2010 R3T is the main support for my rack, without the sissybar the rack doesn't hold together, you'd have to fabricate a couple bars to support it, I wasn't aware Triumph offered a trunk setup, I'll have to check with my bud who is the parts guy at my dealer.
I just added a trunk I got off ebay, its very cheap and not great quality but will do the job required by me. It came with a universal fixing plate which I bolted directly onto the luggage rack. Now I removed the sissy bar and yes the set up was to flimsy so I made up two bits of square bar, 14mm cause thats all I could find for free but 16 or 18 would do too and replaced the sissy bar supports with the new bar. Here are pics.
I have pix on here when I put stb truck on her r3t and hooked her lights up with the quick release luggage rack then when she put her solo seat then changed it to the solo rack
That's a cool looking set up you have, but it doesn't explain how the trunk is attached to the luggage rack. Some people have commented that the sissy bar holds everything secure.....so when you remove it something has to be fabricated to hold things together. Did you make some bracket or something? Is there a bracket between the luggage rack and trunk?