Agree totally--if you use 2-pole 30 amps breakers, you get the benefit of 60 amps vs just 30 with a single pole and a 30 amp RV plug. Think the group think here has concluded that 50 amp 2-pole is the best solution, if you are going to go to the effort and you have a 100 amp source in the barn/shed/garage. But given the anal retentive nature of electrical codes, I still suspect the "book" would discourage connecting a 30 amp 2-pole to #10s and then to a 50 amp plug--just saying.
2003 40' MDTS
Garden Ridge, Texas