Rack mounts are good to keep your gear from burning out prematurely. Almost all audio gear produces some heat, and when you stack two units that produce heat, it increases the heat in each. A lot. And that lowers the life of the gear.
The usual solution is to use something like this:
Those are expensive, and don’t even always keep the units from touching each other, and also don’t allow much airflow, unless you add a fan, which makes noise.
Also, until you get enough units to fill it, it looks lonely and empty and encourages you to get more units you don’t need. And then when it’s full, you have to get another rack and start over with empty slots.
I did my version of this for almost no money. I used stacks of quarters held together with metal furnace tape. Nickels or pennies would even work, but quarters are wider. I recommend using the widest coin in your country that you can afford to use.
I stacked quarters 9 high, wrapped them with furnace tape, and taped them to the desk, and then to the top of the next unit. Now there is airflow under and over all of them,
This is furnace tape. You could use regular tape, but furnace tape will conduct heat better. It will also not give off chemical gas like some plastic tapes would when heated. Here’s the furnace tape I use. It cost 12 USD for 150 feet. Probably more than you’ll ever use. Get it here on Amazon. It’s useful for a lot of things.
The final result looks like this. Note that there are stacks of quarters on the desk as well as on top of the unit on the desk:
I wouldn’t stack these more than 3 or 4 units high, but it will do until you have enough stuff that you need real racks. Or keep using these, but start another pile on another surface.
You could probably do it more neatly than I did, but I don’t care. I’m all about function more than form.