probably best not to use carpenters glue(pva). a better bet might be either polyurethane (which has gap filling ability if the joint isn't a perfect fit), which is wickedly strong and waterproof but, paradoxically, dries more quickly if the glued surfaces are slightly dampened or, a two part epoxy (WEST[for wet epoxy saturation technique] is a good one, which is a very high quality, marine glue). this particular epoxy is fairly 'runny' and so absorbs well and has a good working time (at least 1 hr).
the advantage of epoxy is also it's ability to cure without being exposed to the air. this allows you to place a polythene mask (any old shopping, carrier bag) between the work and the clamp so that things will release nicely when it's dry.
to get a near perfect clamping system you might create a former by first choosing an area on the shell which is undamaged and then make your former by roughing in a couple of wooden blocks which are big enough to cover the repair area, then clamping them in place with car bondo smeared on the face of the wooden blocks to recreate an exact form which you can clamp onto the area to be repaired. again, since bondo itself is an epoxy material, you will need to place a polythene mask between the drum shell and the former which you are making. once it is made, you apply the glue to the repair and clamp the former onto the shell with C clamps.
the ratchet tie down sounds like it might work but, i would try a dry run first to make sure the it will pull things tight enough. also, i think when you glue up, you should put the 'former' clamp in place but, don't snug it up until you have pulled the shell together with the tie down.
good luck.
adrian roddick
December 2007