You might try a dab of Loctite Blue. If that comes loose, then Loctite Red or a small amount of marine epoxy. Loctite expands in any gaps and should hopefully give you a nice friction fit. Clean the surfaces first with some alcohol -- make sure they are dry. Give them a day to set up well.
Another possibility -- tie some knots around the tubes with string or small twine from the inside (accessing from the rear hatch), dab some glue on them and slide them all the way back. This should block the tubes from sliding out the back. Make sure the tubes run through the circular tabs located on either side of your rear hatch.
Let us know how it works!
