While you should contact the US Border Services directly yourself, the way it has been explained to me is that you are allowed 6 months in the US as a tourist within any 12 month period, that is to say a rolling 12 months, not calendar year. Then any absence in order to be deducted from that time must exceed 30 days. All that to say, it is then my understanding that if you leave the US at 5 1/2 months, then return to the UK, you could still have 2 weeks eligibility to return within 12 months of when you initially entered the US.
Confusing at best! That is why you should contact the US government. However it becomes mute if you head home and are not returning to the US within the year.
As a side issue, what are you planning on doing with the motor home?
Ed