Personally I'd think there's no need to sandblast light surface ruststone chips, it's messy and honestly kind of overkill for this kind of smallish repair.
Though not having ever really inspecting your car up that close Jean, judging by your description of the 'rockers' I'd prolly think that a little wire brush stripping followed by a good sanding of the damaged area would be enough. Followed by a good catalized primer/sealer, a coat of gravel-guard )shot smooth if you are going colour match) and a few coats of two-stage basecoat colour and clearcoat would be very solid and long lasting. For those who don't want mudguards, (even though many car I've seen around here came with them factory/dealer installed) another idea would be to apply the clear vinyl tape just at the lower contours of the fenders/rockers.......
Jean, one thing your did not mention is, are you planning to refinnish your car complete, or just respray the lower black areas ???
Ron.