I have done this a couple ways, I have printed the mold and cast that i have printed the part made a silicone mold off that Ã*nd cast parts, the problem is most parts it is not required for them to be cast solid, the resin material is not cheap, and weight is a factor.
I have made a small desktop rotational casting machine that will allow you to cast hollow resin parts. Check out the video http://rotomaak.com
I print prototype models for a large rotational plastic company this way i print one original make a mold and make reproduc5ions