I'm pretty sure they are a standard size. ie.. only one size.
I would take a look at your trailer. As RV manufacturer's tend to switch product lines whenever a better deal comes along. By that, I mean that my trailer and the exact same model trailer built the next day might have different parts on it, that still perform the same function.
20XX 3/4 something TBD
2010 K-Z Spree 318BHS LX