Welcome to the forum, I do not have a Jayco Westport, but I am sure that others with this model will be along to answer your question
If you were to take your spare wheel into any reputable tyre place, they could measure the PCD and by looking up their charts, they could tell you what vehicle manufacture uses those rims.
They could also tell you if you could fit higher profile tyres on your original rims.
Enjoy your stay as this is a very good informative site