I don’t have one of the aforementioned MGs, but this is the first place I look for cases:

https://www.caseclub.com/

Look at hard cases made for large telescopes. They will usually have wheels on one end.

You can get them with pluck foam interiors so they can be custom fit to whatever you put inside.

Driving? Most of us either build a wooden crate or use an original one. Of course flying would likely need something fancier.

If you have any woodworking tools or experience at all, they can be pretty enjoyable to build. Make sure to leave some room for your accessories. Wood rope handles, metal hinges and latches. Paint it up with a nice color. No need to make it super nice finish, just durable.  

Though I think pelican makes some larger cases. Even M2HB size cases. I'm pretty sure OOW offers one for their M2

Turret in the back of a Willys????

look at Used Music equipment Flight cases, like for stage gear and such.
Made of tough plywood, aluminum corners and edges, foam lined interiors. Will have recessed handles and Usually beefy casters too.


Here's One