Have a small C++ prototype app up and running on TWR-K70F120 using MQX 4.2. It uses two message queues. Everything works.
I added RTCS. I can RTCS_create() and ipcfg_init_device() and they return without error. I then get failures on subsequent _msgpool_create().
I'm assuming there's sufficient RAM, just not configured properly. Haven't yet found anything in the documentation yet that helps.