H E R E - CO State Parks Rules and Regs is the PDF of the rules/regs for CPW.
Article 1 #700 Vehicle Pass Section 2 (no vehicle pass shall be required for) subsection .i Any vehicle that is exclusively towed.
The way that I read that is, if you are driving a towing vehicle with a trailer attached, said trailer is exclusively towed. Now some may think that a towed vehicle behind a motor home would not meet this exemption. I think it still does. A towed vehicle behind a motor home is, when it is entering the park, exclusively towed. It is not driving in on it's own accord. It is being towed, and thus exclusively towed, and therefore exempt from a vehicle fee.
It is definitely not clearly written; the gobbledy gook legalese stuff is convoluted. Why can't they just say that a towed vehicle of any type is considered as one unit, and therefore one vehicle fee? Guess that would be too simple...:S