I got an oversized laptop shoulder bag and put the FM-3 in that. Then, I put THAT bag in a Pelican 1535 roller case. There's enough room in this case to put an extra set of stage clothes (in case they lose my luggage), a Boss FS-5L, a Boss FS-5U and a few cables.
Anyway, I roll that Pelican case through the airport. If I have to gate check the Pelican case because I'm on a small plane (CRJ-200 for example), I take the laptop bag out of the case and I carry that bag on the plane. I put that shoulder bag (which has the FM-3 inside of it) in the overhead compartment or under the seat in front of me.
The laptop bag offers a little bit of padding in the Pelican 1535 roller case and protects the FM-3, not as much as foam would, but enough for me since the FM-3 is always in my care.
This method has served me very well for over a few years.
Here's a link to that Pelican case, which I got with no foam:
https://www.pelican.com/us/en/product/cases/carry-on-case/air/1535?sku=015350-0012-110
Hope this helps.