I am a Class A CDL holder with endorsements for doubles-triples and haz-mat, it's what I do for a living. Basically I drag around a 105' long set of Rocky Mountain Doubles full of gasoline or diesel while dodging 4-wheelers with people behind the wheel that probably should have never reproduced in the first place, but I digress. ;D
Educate Yourself In The Name Of Safety
The point that just about everybody that has posted above seems to miss, is that the DOT rules were put into place to promote "Safety". To go blissfully and ignorantly down the road with a substantial portion of your worldy possessions not to mention your loved ones on board with absolutely no clue as to the rules that govern any other vehicle of the same size just because those vehicles happen to have DOT numbers on the door is not a good idea.
Granted the vast majority of RV drivers do manage to get to their destination without any paint transfer but....why not avail yourself to all the information that is out there on the off chance that it might just save not only your life but somebody elses. The fact remains that just 'cause you can do it legally doesn't mean it's smart.
I personally encourage ANY RV OWNER to go to DMV and at the very least pick up a copy of the CDL Class A manual and not only read it but study it well enough to pass the written test. Unfortunately, most states won't let you take the CDL test without a valid medical card which means you'll have to chunk out about $100 for said card if you really want to take the test. On the other hand, if you can't pass the DOT medical (about all that's required is a pulse), you really shouldn't be behind the wheel of ANYTHING in the first place.
Insurance
Should you go get your CDL you might also find that your insurance company believes that you are a lower risk and drop your rates.
Liability
Most of you reading this have spent the better part of your life preparing yourself for self-sufficiency and possibly a carefree retirement. Now imagine that you are driving your Class A motorhome that weighs in at more than 30k and the unthinkable happens, you get involved in an accident and somebody dies. You need to realize that the victims attorney is going to take all of that away if they can find ANY reason to blame YOU for the fatality, regardless of whether law enforcement has cleared you. You don't even want to consider the consequences if you are found at fault or possibly negligent because you had not made the effort to ensure that you were properly trained to operate the land yacht of your dreams.
Sorry for getting up on my soap box but....I have had TWO class C RV's collide with the tanker that I was driving in the last five years. Neither one of them had any idea when they got up in the morning that a poor decision on their part later in the day would put their life and that of their spouses in grave danger.