• Stop. Don't drive as far. Use the weekly rates in a campground. Make sure that it is not too far to the nearest town, however. You will need to get groceries. "Free" Campgrounds is a booklet put out by Camping world, and there are also some quite inexpensive ones. You might consider Quartzsite, Arizona, or the Rio Grande Valley area near McAllen, Texas.
• Eat in. If you eat out, lunch is less expensive than dinner. Bring home the leftovers. Use the Sunday papers to find the grocery coupons. Eat at casinos, their food is usually quite inexpensive. Utilize farmer's markets and roadside fruit stands. Try the senior meals at the senior citizen centers. The early bird specials are usually the best deals.
• Insurance. The fulltimers all agreed that this is a problem. For RV insurance, when you are fulltiming, a company which specializes in RVs is better that a State Farm or the like. Health Insurance is expensive, as HMOs can cancel the fulltimer. Sometimes, a hospital will work with you to reduce the cost of your bill. Be wary of having too many tests. Be your own advocate, read your policies.
• Gasoline. Some fulltimers mix premium and regular. The amount of weight in your RV is important. Every 100 # of weight increases gas consumption by 2%. Don't use your dashboard air conditioner.
• Use Golden Eagle, Golden Access and Golden Age discounts for visiting National Parks and Monuments.
• Cut down on phone calls. Get the kids to call you. Use a major telephone carrier (as some smaller companies are very expensive) and know how to access it from any pay phone. Some prepaid phone cards, Good Sam's and Escapees, are worth looking into.
• Fulltimers do not need an extensive wardrobe. Get washable, not dry cleanable clothing, wash it with half the amount of soap and fabric softener in full loads and with the minimum amount of drying.
• Entertainment. There are many free museums, early bird movies and senior discounts on entertainment. Local libraries will issue short term cards.

There are as many different answers as there are fulltimers. Try it -- and you'll soon develop your own list of ideas and suggestions.