None of those sites that list length, doubles etc are ever right. The only way is to contact each state individually and even that changes so often you might not ever be right. Nv rv was 75ft, now reads 70ft, used to be needed endorsement for doubles now you dont or do you ? Might have changed today. No overall length limit here for trucks but they limit trailer lengths. Can go to 129,500 lbs with the right combo. How in the world could you ever know whats right in your own state let alone in other states.
Careful with the entry level DP's as they dont have alot of towing capacity. My Tiffin Red doesnt leave much after you load the coach. Its quite easy to end up over gcwr with the transmission being the weak link. Find one with 3000 series Allison and your good to tow.
I think that most people just dont research when buying. I have talked to people that were shopping for a used truck and had never even thought about a new one as they thought they couldnt afford one. The used market place knows this and takes advantage of it.
DSDP, my Cat backhoe sits for months at a time and then gets its neck rung out without additives. Other than some Howes when it gets real cold i have seen no need for additives and probbly dont need that but it gives me piece of mind when its 20 below.