My thoughts are that he actually did a terrific job with the RV.
The RV wasn't working when our heroes decided to fortify the motor inn. When Kenny wasn't out hunting, scrounging for supplies in Macon, or stroking that strange pipe in Episode 2, he was repairing the thing. Yes, he was planning to take his family and leave with it IF he could get enough people to come with him, but he realizes that if the rest of the group wants to stay he will too, as splitting up would be a dumb idea. Kenny said he got the RV running again, he didn't say how well. In fact, he was still working on it during the raid! If it had been truly road-worthy, then everyone would have been out of there just as the walkers showed up, instead of when they were already past the wall. Even Lee doesn't truly believe that it's running when you inspect the RV while searching for the missing supplies. Just because it wasn't COMPLETELY fixed doesn't mean he was irresponsible. In fact, if it hadn't been for him fixing up the RV it's likely that no one would have made it out alive. If he had had more time, I think he would have completed the repairs, or at least come as close as he could.