On the surface, RV living seams cheap. There are hidden costs. With three small children, you will spend $20 a week just at the laundromat. The lack of storage and small refrigerator means you cannot take advantage of grocery sales and stock up. That could easily cost another $20 a week. RVs are energy inefficient. Most long term parks require you to pay for electricity. Propane to heat in the winter will be expensive- RV furnaces are horribly inefficient. This could easily add up to another extra $20 a week over conventional housing. This is over $3000 annually in extra costs.
There are only two problems with any finances: not enough income or too much spending. Most families suffer from both. You would be better off obtaining conventional but cheap housing to save money while finding ways to trim your expenses and increasing your income. (Hint: you don't need two cars both with payments!)
Dave Ramsey, as previously mentioned, is extreme but it works. That is a much better approach than a $55,000 RV!