Side gates are great, just because you don't see it does not make it so. Two Walkers . mulch on front , bag on back, both blocked and strapped. Playing musical chairs with 700-1200 pound mowers like you say is is not going to yield a 8-10% tongue weight when you start moving them around for the next job. More equipment gets destroyed in transport than cutting. Each mower needs a spot, needs to be blocked(by law) and the trailer load needs to be balanced for tongue weight. . Swapping mower positions will not cut it . A side gate does not cost 2-3K.