Place all the images and the LR catalog file, Preview and the like on an external drive. Move that drive from Mac to Mac to edit, view, whatever.
All you have to do is point LR on each Mac to look for the catalog on the external disk.
From my understanding, I could just keep a catalog on my portable hard drive, but I don't want to face an issue where that hard drive could be lost or damaged and my entire catalog is gone.
Yes, this would work, and is a good solution when you keep switching between computers. Equally, you identify the main risk.
So, each time you use the catalogue, can't you back it up before disconnecting the drive?
Will this keep the catalog that is on my RAID up to date?
I don't have a problem just going back and forth with my catalog, but I want to make sure I have a solid backup at all times in case something happens to my portable hard drive
No you have to do that manually or with some type of backup, second copy, utility. Please note that the catalog file can't be used if it is located on a network drive. It has to be local to the computer that is running LR and trying to access it. By local I mean a drive connected directly to that computer, internal or external.
Let me ask you this. If I simply select the photos I want to edit on my laptop and go to File and then Export as Catalog, save that catalog to an external hard drive and open that external up on my laptop, that should technically work, right? I just tried it and it seemed to work and opened perfectly on the laptop. The only concern I have now is when I import that catalog back into my desktop, how do I bring those photos back into my original catalog with all the changes I have made? Also, will the original catalog (desktop) keep all the photos that I deleted when on the laptop? I'd obviously prefer if, when I brought the new catalog (laptop) into my old catalog (desktop), it would remove all the photos I had removed from the laptop. Does it do this?
Yes exporting as catalog will work and then Export as catalog on the notebook and import catalog of the desktop Mac.
But I've never had the need to do this although I do have both a notebook and a desktop and have LR on each. I have one catalog on the notebook and a different one on the desktop and never cross reference them.
I do very little editing on my notebook. About the only thing I use LR for on the notebook is to keep track of shots I've taken while traveling or jobsite images. Personally I don't understand how anyone can do any good editing on a notebook.
When and if I do some editing on my notebook I have the option to Auto write changes to XMP so when I get back to my deskopt and copy whatever images I downloaded to the notebook and then import them to my desktop install of LR, LR will read the XMP files.
This is a classical. You find a lot of answers to this problem in this forum:
Laptop and external disk (2TB) for mobile shooting.
I import the catalog (and pictures) from the external disk to my desktop (6TB).
The desktop gets backed-up to my NAS (18TB).
This config works fine for me. Only draw back is, that the publish services are not synchronized.