I don't carry any spare (no location I would be comfortable doing so), but I am VERY intentional about thinking through fueling and have planned out stops for my upcoming trip (WI to FL). With a 35' tt we are limited in what stations we can use, and I need to fill every 200 miles or so to avoid getting below my comfort zone (37 gallon tank at roughly 7mpg). I hate having to fill 3x per day on long trips, but it is what it is!