Well I have no experience doing this wile covered, but I did mine uncovered. So recommendations play some loud gospel music, (covers what u might say from frustration) some good knee pads, flex and loosen up for all the fun positions u have to bend in. Well you get the idea.
Actually I understand it can be done, my best suggestion is get a good wool headliner (not from aircraft spruce) so once you give up on a nice tight fit you can shrink it to look better. Remove rear windows cover the interior in case you spill or drip glue. Buy some clamps more is better and take your time fitting before cutting or applying glue. There are several post of different folks doing the headliners with picture. Hope this helps and good luck please post some pictures of before and after.
