We are shopping for a 5th wheel to fulltime in all over the US. Concerning 4 seasons insulation, how cold can you use these without a skirt, and with a skirt - before lines start freezing? What other problems with the RV are we likely to encounter winter camping? Are all the manufacturers "4 season" insulation packages pretty much the same, and what should we make sure it includes (heat blankets on tanks, heat tape on all lines, etc.? Thanks!