while the Prof is of course right, in these matters, I do wonder sometimes why such questions are asked in such a vague manner, ok so their new. new to caravanning and new to forum but still.
all the info is out there on the net, look for it, Research,Research,Research,Research,Research,
and when you have got the answer then ask a question, dont expect someone else to do it for you.
it is like asking how long a piece of string is.
the answer to that and the OP question is the same. 42. anyone knows that.