Re: tag axel
I would agree with s.harrington. That is espceially true for a class C. The advantage is quite simply that it gets you by with a condition that would be overloading of the chassis if you did not have one. But the problem is that no class C chassis was designed for the use of a tag and all of them were added on by the RV manufacturer. The extra axle is just what the name implies, and axle that "tags" behind the drive axle. The tires will scrub when you turn so they won't last as long as the other tires on the RV. Another down side is that you now have eight tires to deal with, rather than six. Quite often, there is no brake on the tag and those that do have are very often of little use. That will mean extra load for the origional brake system. There are some owners who claim that the extra axle and wheels add some degree of stability. Not sure if that is valid. Reviewers will tell you that the tag can cause traction issues when traveling on wet or slick roads or on unpaved ones.
All of this comes from reading as I have never owned a motorized RV with a tag, and I never will.