Hey there,
Not absolutely positive, but I think that your generator is designed for connecting to a 120/240 volt panel, and in order to use the 40amps @ 120v, you need to balance your loads onto the two 120v legs.
Basically, how a normal house breaker panel works, is you have two lives and a neutral(ground) coming into the pannel, where between any of the two lives and the neutral, you get 120v, and between the two lives you get 240v. So, this means there is not way you can join the two lives to double the amperage @ 120v. All you will get is lots of sparks and blue smoke!!
I believe you were asking if you could parallel the two ordinary 120v plugs, by connecting the two live and the two neutrals together, but, I don't think this will work, because they are probable the two different lives, and instead of getting more amps, you will simply short out the 240v cirvuit. To check if this is the case, start the generator, take your voltmeter (AC), and check the voltage between the two lives, and the two neutrals, and the only way you can connect the two is if there is not voltage between the two lives or the two neutrals. It is very unlikely that you will be able to connect them.
The better option, I think, is to check the pannel in your RV. If it is a 120v pannel, designed only to be plugged into a 120v source, and does not support 240v devices, you should probably think of replacing it. You should get a small 120/240v house pannel, which will support the generator, allowing you to balance out your 120v loads between the two 120v legs, and will even give you the option of adding 240v devices to your rig.
Anyway,
Hope the helps,
Cheers,
Stephen.