plastic v. porcelain toilets

The existing porcelain toilet has cracks along the base and it is leaking. Cannot use a newer, higher toilet because of the design of the bathroom. What are the pros and cons of porcelain toilets v. plastic ones? I would prefer replacing the existing one with a porcelain, but having real problems finding a new one that will fit. Are porcelain pottys prone to cracking in an RV? Thanks.