Let me try and find an Inverted V dipole in an attic. Could you use 5ft firestick antennas then?? If so that would be the great. The 5ft long firestick antennas appear to be a pretty popular antenna for the attic installs with not a whole lot of room.
Let me find a pic of the bracket that someone made for using an Inverted V In the attic. Looks like what was used was 2 stud mounts, and a piece of steel strap with 3/8" holes in it. You can see the rest and hopefully get an idea as to what you need and how to make it. You want to keep the legs anywhere from 60-120 degrees. You can hang it up on the peak of the inside of the roof with a coat hanger. Seen that done as well. Or do like the one in the photo and place it as high as possible. Hope this one helped more than the first one.
And like I said before. Stay away from anything shorter than 4-5ft long as far as the antennas go. I think Wilson might make a similar antenna as the ones used in the pics. But I am pretty sure those are firestick antennas. Either wjll work.
Have a good day and hope you get something figured out.