Hi Steve,
Assuming that the images are aligned, then you first need to split the RGB image into the three individual channels. You can then use LRGBCombine process to 'add in' the L image, along with the three RGB images.
If you want to add-in the Ha image, then there are tutorials that will help you achieve this as well - or, you can try doing things yourself by using PixelMatch to mix the Ha with either the Red image, or with the Lum image, or a combinations of both. You would still need to recombine the LRGB channels as I mentioned above - even though you may now have 'modified' versions of the L and Rd channels.
There is also nothing to stop you applying the same process to any other narrow-band filtered images that you may be able to generate.
Hope this helps.