On our last rig we also had the manual awning. I would stake each end to the ground using anchors, springs and chinch straps. I also would put Awning De-flappers
(2 per side) on to keep the fabric from flapping.
One other trick I saw another RVr do in a park one time is on the upper collapsible bar, he drilled a hole through the two bars and installed a hitch pin to keep them from collapsing. Most of the time when the wind comes up it isn't the initial flapping that causes damage it's those arms collapsing and allowing slack in the fabric which then allows the fabric to "whip" harder.
Doing this all would only take me about 10 minutes to set up but I could leave my rig even at the coast with complete confidence that it would be safe. We saw VERY high winds during storms and never a problem with it secured this way.
We now have the automatic awning and I wished I still had my old manual one so that I could leave it out in bad weather and not worry about it.