I'd suggest taking that primary condition's rating and attempting to connect any secondaries you've got before appealing but still stack evidence for a supplemental.
There might be smaller disabilities you haven't thought much about because they're not a major hassle in our lives yet, like:
- GERD, especially since PTSD meds might trigger acid reflux
- Prostrating migraines from the stress that anxiety causes
- Sleep apnea, with PTSD throwing causing sleep disturbances
Worst case, in my opinion, and if they apply to your life and you can get them service-connected, you get two 10% disabilities from those and move up to a combined 80% rating.