bummers. i've had similar problems with pvc end caps cracking and splitting. just got a longbow last week and the cap was split along the side during transit and luckily held in place via duct tape, and the seller used a good tight wad of foam to secure the limb tips.
when i send a bow out in a pvc tube, i wrap the tips in either foam or bubble wrap, then make 3/4" plywood discs to fit inside the tube ends, secured with 4 screws around the tube end perimeter. the ends are wrapped in duct tape for added insurance. still, ya never know with any shipping vendor if they'll hand off yer bow to a 500# gorilla ...