I looked your B&S Genny Manual up
HERE.Link may actually bring up Page 11 which states the following about the Locking Outlet:
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This receptacle powers 120/240 Volt AC, 60 Hz, single phase loads requiring up to 5,550 watts of power (5.55 kW) at 23.1 Amps for 240 Volts or two independent 120 Volt loads at 23.1 Amps each. The outlet is protected by a push-to-reset circuit breaker.
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There's a diagram of the locking outlet on that page. Looking at this, you CANNOT make max power of 5500W available at 120 Volts, which is what you need. You are limited to half that, 23 Amps, on each of two 120 Volt legs of the generator.
You can't "stack" them and still be 120 Volt!!!
Somebody who knows what they're doing could wire a 30-Amp RV receptacle to ONE LEG of that Locking Outlet. A mistake will send 240 Volts with the consequences you're rightly worried about. Since you can only get about 20 Amps, just use a dogbone adapter to one of your 20A duplex outlets.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB