I have my '66 chevelle parked in the garage and cannot move it since i have my motorhome outside parked behind it, which is winterized and covered up for now.

Just last week, I noticed quite a bit of trans fluid spatter underneath the car on the floor. Can trans fluid just start leaking when the car isnt moved / driven for months on end. I prolly havent started it in over 5 months now. (battery is disconnected)

Is this a common thing that can happen to cars that just sit without movement to start leaking like this?

Its definently not oil, its a slight reddish color so im thinkings is the trans fluid.
Poor car seems to be bleeding to death lol

They can, usually it happens sooner than that though. The trans will drain back some of it's fluid back to the pan, and maybe overfill the pan, and start coming out the pan gasket, or the dipstick tube seal.

Not sure if your car is parked on cement but I was told if that is so you should find some rug to put underneath.Not sure why but cement tends make seals dry out.My speedo cable was leaking I just had to replace the seal there and no more leaks.You could also put your car on jack stands