There is no 'one size fits all' answer to this question as it will depend on the time of year you are travelling and how much you use components in the RV that require propane.  Propane usage can increase significantly as temperatures drop.  In extremely cold winter temperatures, it's possible that you may need to refill your propane every other day but in summer, the tank will last significantly longer.  It is important that you monitor your propane usage daily, regardless of the time of year, and never let the level go below 1/4 tank.  Know in advance where you will be able to top up the propane tank along your route.