Wow cross country I have never done. Good for you. 50 lb trailer yea that will be hard to drag period. Must admit I do not know Aguanga but I have ridden many roads on your first part of the journey ie Warner Springs to Brawley.

You will climb the question is what route take the 79 through Julian or Montezuma to Borrego or Ranchito to Ocotillo wells

The x factor in the Anza Borrego is always the wind if it is in your face (less likley) or across you (more likley) a trailer will be tough. When the wind blows in this area and it often does it can be brutal. For me hills, mountains are not an issue as they eventually end. I have climbed enough over the years to understand and succeed at climbing. The wind of the desert is another thing. Insidious unpredictable and out right demoralizing. The Anza has beat the hell out of me more than once. I prefer hills over wind anyday.

I have never toured more 500 miles but would always prefer the weight on my bike and as little as possible.

You will be in some pretty remote areas to begin with so I understand your need for gear food and water. Since you have done this in the past I assume you have that dialed in. For me route planing would be essential for reloading supplies.

You should post pictures as you go. Always wanted to do this, maybe one day

Good luck