this is a very good but extremly time consuming strategy. i often use medium ships (~cruiser) for that - i load it with normal BR,LS,CQ, then Ion Engines III and the rest with the miners. Then i set orders - go to site -> sentry -> go to ressuply -> repeat orders
and you can forget about it, just check once in a while if it is producing less than it is costing.
Also, if an enemy comes in simultanous, the ship will just break the sentry and go to the ressuply post - probably better defended, and will effectively dodge any possible combats
