Yes, I use an Endurance Side Case as fitted on the Stanley Special and the Country Trekking Cub House specials. I bought it from Beezdeals and it is top quality, and will carry fishing rods, beach umbrellas and even a pair of 2x4s if you are brave. It is very well constructed and is of high quality. There is no room for a rear rider when the case is mounted, but it does clear the rear foot pegs when the pegs are folded up. You can unbolt the case from the mounting bracket and leave the mounting bracket installed if you want to carry a passenger. The topmost part of the case makes a great handle when you want to move the motorcycle around the shop. You have maximum advantage when using the top of the case as a handle.
I notice that Beezdeals doesn't list the Endurance Side Case any longer, but lists the Revolution Side Case instead. I don't know if Revolution bought the design from Endurance, but the rivets in the cases are in identical locations. The mounting brackets are slightly different, but the bracket designs are similar and use the same mounting points. Here is a link to the Revolution Side case on Beezdeals:
https://beezdeals.com/product/revolution-side-case-honda-trail-125-ct125/
Webike may still be selling the Endurance Side Case. Here is a link to the Endurance Rod Case Kit, so you can compare the photos:
https://japan.webike.net/products/24465227.html
I also question why a crate seems to be the first choice of a rear carrier for many first time Trail 125 buyers. Is it nostalgia bringing back the crate look of the old times when proper top cases didn't exist, and the budget was 50 cents for a case? For me, a rear top case should be rainproof, not transparent, lockable, but locking is not required, and large enough to hold my helmet when I am shopping.