I've got the 40 as well under the roof. The 42 would not fit how I mounted the 40. I used the feet but if u removed them and figured a new way , maybe so. I didn't want it on too for fear of rolling and crushing.
Yea I was gonna say a 42" would be super tight but depending on your mount, it should work. There's a bunch of clamp mount kits out there. I've got a 40" mounted directly to my emp aluminum roof. I've got a buddy that has a 40" that is clamped to his cage. Looked like there was probably room to spare another 1" on each side to fit your 42"