I haven't but many have.
Having the intestate fender struts, trunk, lights, pass. backrest is very nice, but not cheap.
To get any kind of size, I think you need to make a bigger base to add to the luggage rack for support. Lightweight aluminum seems to be the best solution.
Mike (hubcap) has a big Givi trunk for his Tourer. Some of those have lights.
Also, you don't say if you carry a back seater, because if your don't, you can pull the back seat and move the trunk forward to that position (can even be a driver's backrest). It can carry a lot more weight in that position, than hung out over the back of a luggage rack.
Some of the cheaper smaller trunks look pretty flimsy to me, but it's what will satisfy you (and not anyone else) that matters.
I have two interstates. One is permanently trunkless, and that one carries more gear in a big waterproof dry bag (in my back seat position), than will go in an interstate trunk. BUT unlike a trunk, my duffel(s) do not lock. So if locking security is what you want/need, make sure it will carry what you want to lock up, like one or two expensive full face helmets (if that's your goal). No sense going through all it takes to mount a locking trunk if it is not big enough to carry what you want to carry in it.
If you do not need security, beyond your locking Tourer bags, why go to the trouble of a truck, just get a big waterproof duffel (or sissy mounted backpack). Mine is designed to take all my clothes, toilet, tennies on a trip; so as soon as I get to my destination, a bunch of bungies (and bungee net) comes off, and it goes in the room for the duration. All my security/value stuff goes in the locking bags, and stays in there.
Something else I learned, if I pack a big duffel on the back seat of my trunk interstate, I can't open the trunk when it is sitting on the back seat (at all). I never carry a back seater, but I can't carry much of anything on the empty back seat on that bike, or I can't get my trunk open while riding loaded up.
But, not all aftermarket trunks open rear to front like the interstate.
Another thing. Lots of Harley tour packs (in different sizes) can be had for relatively cheap, for pretty good quality (though fiberglass weighs more). If you can live with a Hog trunk on your Valk, they are probably some of the best for the price you can find. They'll also require you to mod up a mount.
https://www.tsukayu.com/TouringTrunk.htmhttps://www.revzilla.com/motorcycle/givi-v47-tech-monokey-topcase?kclid=21297cbc-66f7-4715-a9a3-15695abfa9c1&gclid=EAIaIQobChMIlOLx-OXt2wIVF1mGCh3qsQ4CEAQYBCABEgJ_F_D_BwEhttp://www.egobikeusa.com/product/db01-black-motorcycle-trunk-luggage-case-tail-box-rack-backrest-for-harley-touring/
https://www.saddlemen.com/hc2900-hard-case-trunk-large-universalhttps://www.google.com/search?q=motorcycle+trunks&client=firefox-b&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjmqrXO7e3bAhUtuVkKHVkXDskQ_AUIDCgD&biw=1424&bih=652