Max trailer length

tom O, the rules for commercial vehicles also apply to recreation vehicles. These allow 53' trailers on all National Network roadways (interstates and federal highways), plus "reasonable access" to/from fueling stations and delivery locations. (Information can be found here: https://ops.fhwa.dot.gov/freight/publications/size_regs_final_rpt/index.htm#rv).  Individual states may limit trailer and/or overall length on smaller highways and local roads. 

Are the shorter-trailer rules ever enforced? Sometimes.

I know that California has a lot of state highways where trailer length is limited; also the distance from kingpin to the center of the trailer's axle group. And these get enforced! So be informed before pulling a long trailer there. 

- Old KW Guy

I don't know the answer but like you found in your research something doesn't seem right about the length law in Indiana if the majority of the RV's are built in Elkheart.  But that being said if the law in Indiana says 40 feet I wouldn't count on a cop just looking the other way. The real question is would you ever get pulled over and measured. My guess is no. But that's a guess from a guy sitting at a keyboard in California.

I know its not going to be the same but up here we have a max overall length of 65.5 feet.  so as long as your under that it doesn't matter what your trailer length is.  not saying we don't have a max trailer length in conjunction with that overall length but if there is I can't find it.

So let’s say I have a 41-foot trailer and I tell you ‘in 10 years I’ve never once had a problem’. So you go out and buy a 41-foot trailer and every time you pull it out of the driveway you get a $125 ticket. Then what?

You can’t count on breaking the law without consequences; regardless of anyone else’s experiences.