San Diego to anza borrego state park

Notice the edit! I do not remember the precise road we used, but a few years back we did a day trip in my wife's XC-90 from the wine country in Temecula to Anza- Borrego. The grade we took, I would never do in our 37' Class A. One of the RV parks had a sign warning of the grade. They told me they verbally cautioned people about it. I think there is a high probability that the above recommended route has you using that pass. On our return trip we came around by the Salton Sea back to Temecula. A lot longer, but it is what I would do from Temecula in an RV. Might I suggest you call the park you are going to, or contact Cal Trans or the CHP office that has jurisdiction in that area to be sure.