A portable trailer stabilizer, comprising: (i) a support surface engagement element configured to selectively engage a support surface; (ii) a trailer engagement element configured to selectively engage a forward end portion of a trailer; (iii) a hydraulic cylinder operatively connected between the support surface engagement element and the trailer engagement element, the hydraulic cylinder configured to extend the trailer engagement element relative to the support surface engagement element; (iv) an on-board, self-contained energy source comprising a hydraulic accumulator operatively coupled to the hydraulic cylinder; (v) an isolation valve fluidically interposing the hydraulic cylinder and the hydraulic accumulator; (vi) a positioning element engagement element configured to selectively couple with a trailer stabilizer positioning element of a tractor; and (vii) a valve operator mechanism configured to (a) open the isolation valve when the when the positioning element engagement element is coupled to the trailer stabilizer positioning element of the tractor, and (b) shut the isolation valve when the positioning element engagement element is uncoupled from the trailer stabilizer positioning element of the tractor, where the hydraulic cylinder, the hydraulic accumulator, and the isolation valve are operatively connected in a closed hydraulic system containing a hydraulic fluid.