Thought I'd add to this thread as seemed better to keep similar info/ideas on one place for people looking searching
Finally finished my C rail setup. Didn't want to stick and/or drill permanently to roof so came up with idea of utilising the roof rack mount points in combination with the suckers I've been using to date.
Previously I've just been using the 3 awning straps, 1 attached to each sucker, which has worked fine other than leaving a gap between the vehicle roof and the awning door 'lip', creating a bit of a wind trap, and certainly not water tight!
New solution has the C rail tight against vehicle roof ( 2mm rubber strip/seal on underside of C rail).
Yet to be tested 'in the field' but seems pretty sturdy so far...
Slightly inconvenient is the fact that the distance from front roof rack mount to centre one, is different to the distance between centre and rear, and as I wanted the flexibility to attach either side (depending on campsite conditions), I cut in some slots to allow outer mounts to slide forwards/backwards to suit.
These areas were reinforced with thicker aluminium (JB Welded) to C rail, otherwise a decent breeze will probably just bend the rail.
If it turns out not to be strong enough I'll have to opt for 2 separate bolt holes, which was originally my plan but imagined it might be a bit fiddly moving brackets in the wind and rain!
C rail is 2 x 1m section, that fold in half for storage
