As the guys have mentioned RT bags are a great idea.. keep all your crap dry.
On my single the bottom has studs along the edge which the top clips to so when rolled up its sort of sealed..
If it's raining I rolled mine up then into a tarp..
Then strapped down..
But now I have a RT big..
Much easier..

Fark it I'm gunna beet clunk..
@AB..
Where are the redback roof top bags!!!