Travel in Motorhome? Buy Coats in Tas? How Cold in March?

we, (two adults two children 14,11) are travelling tassie in march 16th for 17 days. is it better to take a car (45$/day) and caravan parks of motorhome(150$)? can we access most places with a motorhome? how cold is COLD in march? would it be advisable to buy coats in hobart when we arrive? i have read the 60 best walks of Tasmania and cant wait to walk until we drop. It the weather so cold as some have written on blog sites??? Help needing to get preparations underway.