A30 or A38 into Cornwall

I am traveling to Cornwall Sat 4th August. I haveboot towed a van there before. I know it will be a long journey but trying to decide the best way to tackle it. Where to set off really early Sat morning when hopefully traffic will be lighkid family can sleep in car and hopefully get some miles done before we hit traffic. Or set off tea time Friday, dohalf journey and try to find somewhere tpip ark up for the night and finish the followingmorning. Also best route to take A30 or A38. traveling from Rotherham to St Austel.

Any suggestions on what worked for you welcome and if a prolonged stop where you did so.

Thanks

David