I use a 12 inch co-axial University bass reflex , nicely built wood , corner style cabinet . Built around 1957 and it sounds great on the GPR-90s as well as the NC-183D . Another favorite is the big Hallicrafters R-42 , also a bass reflex . Good for use hours on end without a trace of fatique .
I have an old RCA drive in movie speaker (the old hang it on the window , jump into the backseat type) that is used as the monitor for my little 2 meter rig , sounds real good for the limited audio from the Yaesu FM rig .
Drive in speakers are fantastic for what they are.
Weather proof, shielded, and durable.
They do have the odd "hook" and cheezy finish/color.
The hook makes a good rest for a desk and simply clean and prime it.
Take it to your local body shop when they are spraying a color you like!