Er, there's still a lot of reasons to use lsbox. It's much easier to use, it's actually designed to be used that way, and it can load older modules.

And really the only tricky bit with systray here is getting a notice when it hooks into lsbox. You can actually do that by understanding the syntax of box hooks and writing a mzscript bang to emulate it:(will need adjusting if you use userdata)

Then you just need to keep an absolute value for the desired size/position that you update in OnAdd/Del, I suppose you can probably figure that one out. ;)