Re: tag axel
Sure, you may be able to get tag axels which can steer or lift off the ground, but these are additional mechanisms which need maintenance and can break.
As mentioned, a Class C (van) chassis was not designed for a tag axel, so adding one may not be an optimal design choice. On a chassis specifically designed for tag axels (some class A or bus chassis, perhaps) it may not be as bad an idea, but make sure you really need the exra weight handling capacity and it is worth the additional problems.
2 other negatives to keep in mind - the tag axel cuts down on storage space, and on toll roads, may cost you more (particularly in Tollklahoma
)