The cl-raylib bindings are what I'm using right now. It works pretty well. Sadly, the one I'm using does not have raygui support. There is claw-raylib but it looks a bit setup intensive.
I don't think you need to rebuild SBCL, you can run SBCL with "sbcl --dynamic-space-size 32000" and you should be able to use Trial. Trial is awesome but it's not something you learn in 3 days. Sadly the API changed a lot so it's hard to look at the older game jam examples which where written in an older version of Trial. On the other hand you have a released product to look at with the Kandria source code, but that's a real project with a huge code base.
trivial-gamekit is something worth looking at, and if you want more features there is cl-bodge which is the 'non-learning version' of trivial-gamekit.
I'm probably switching to Trial aswell, I made a small project a year ago with it. I hope nothing much has changed. :D
Edit:
I just stumbled across EON (https://github.com/bohonghuang/eon) which looks really nice if you are able to build the claw-raylib bindings. Maybe I take the time to do so, because it looks like EON will take most of the pains away you get when using raylib as a standalone thing.