Hi folks recently moved from trailer tent to a 1998 lunar solar 524. we have been away once already but are looking to buy a full awning for the summer the handbook says 979 ground to ground but i have been told to measure as this can be innacurate. how do i measure? some sites show to go right round the awning channel others say follow the line of the van at the front in an A shape! Sorry to ppost a question as my hello but im vexed.