Idea: take a 2x4, or a board wide enough to put under one of the end cross legs,
can't tell the width for sure from the picture. Attach an axle rod the full length of the board and add wheels like jaromp displayed. Put side boards on the axle board creating a cradle, then place it under one of the cross legs. Lift the other end and roll it where you want it, then remove the axle/cradle by lifting the cradled end. Non-permanently attached solution.