the sc10rtr (2.4ghz) I bought actually has a full length antenna tube, but the futaba 2PL 2.4ghz RX's I bought have such short antennas that there's no way they fit in a full size tube. Is there some length that should be in a tube, and the rest can be safely tucked away? I don't really want to cut an extra whole in my TC body if I don't have to.

i just zip it the tube on to the chassis and its all good

The 'antenna' is the diff looking piece at the end of the antenna wire. That's the piece that needs to be up in the antenna tub near the end of the tube (pg 12 in the manual). If you leave it down on the chassis, make sure you do a range check to make sure you have adequate range before finding out the hard way you don't.

If range check indicates you have plenty, you're good. If you wind up with a reduced range, you'll have to try something else with the antenna.