I think you want to put a DP switch in the shore line between the cable and the panel. Answer is yes/no. you could, but if you forget to open the switch once, you may electrocute someone who may grab the plug end. You really should use the proper switch. Simply put economics away, and do it right. A double pole double throw switch isn't that expensive and considering that you only have to flip one switch, instead of remembering two...well I'd say its a no brainer.
Why don't you run the #10 wire to an RV outlet box mounted inside the shore power cable compartment? then you could just plug the RV's shore power cable into that when the inverter is needed?
2000 Cherokee 29BH with 6V batteries, LED lights & 400 watts of solar power, flipped axles and raised. 2007 Tundra 5.7L DC-LB with lots of mods. C-co, 8/158th AVN Maint.