Since you can only pull (basically) 30 amps from your home 30 amp supply, your current cables designed for 30 amp (10awg) are sufficient safety wise.
However, you do not mention how long a cable run that is to the street to your RV. There will be some line loss of voltage. The more 50amp 8awg cable used, compared to the 10awg, will result in less line loss. I don't have the link handy but web search "AC line loss calculator" and you will easily find it. You can add the losses up separately for each length of different diameter wire.
