A 1974 Duster - My 2nd one, 41 years later!

Yes, I'll lock the casters on both sides, closest to the car. I am also going to bolt on to each side of the scaffold just above the casters a 2"x4"x8' stud/piece of lumber that will stick out under the car (the end will be touching the garage floor) , this will eliminate the chance of it tipping over as I lean out, into the center while painting the roof.