I would also look for RV parks that allow park models. Park models are better insulated and therefore you would pay much less for utilities which will be expensive in the summer. When you are in an RV park long term, as you will be, the electricity you use is charged separately. There is also more room in a park model for you and your kids.
If you will not budge off the idea of a fifth wheel, purchase an older one that is of better quality rather than a new one of lesser quality. You want one that is built well, with good insulation and quality components. Getting a new one with a warranty is not going to compensate for poor workmanship. Also, as stated, where are you going to live while the RV is in the shop for warranty repairs?