if your trailer is only 30amp there is (really) no benefit to a 50amp surge, as a 50 amp coach uses 2 120v legs and your trailer only has one....so even if you plugged into a 50amp outlet with your 50-30 dogbone, your only getting the one leg.....
just buy the 30...its cheaper and it will do just fine...(tho you still may want to use the 5-30 dogbone)....sometimes those are a little less worn
2015 F350 Platinum Fx4 6.7 Diesel Dually. B&W turnover, B&W Companion, air bags and wireless controller.
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2012 f250 Fx4 6.7 Diesel crew cab tinted n tuned
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