Apparently not.
Your arguments so far don’t make sense to me, hosting H20’s, PLARF, or floods of Diesel Subs as you suggested is just not realistic imo, why would Cambodia agree to that? Have you considered Cambodias point of view at all? Or ASEANs? Or Chinas past modus operandi?
My arguments:.
1. There is no threat in the Gulf of Thailand.
2. A strong Cambodian Navy can defend its maritime territory by itself.
3. China can already cover those waters with rockets and subs and god knows what else.
4. It’s adjacent to the SCS, which China can easily deploy from, doesn’t even need a support ship.
5. It’s in the first island chain, surrounded by friends and neighbors.
6. It doesn’t protect anything.
7. It would just be an easy to target for nearby western forces, easy to destroy or blockade.
8. China said they are not.
9. Cambodia said they are not.
10. Geography, the Thai ismuths blocks access to the Indian Ocean anyway. China can’t sail through it or fly over it, they might have US SAMS deployed there.
Whether Cambodia will allow it in the future is one question. Whether this would significantly help china is a different question.
For the first question, that's up to china to negotiate with Cambodian government. You may ask why would any country in Asia host American base? How would it help them? Clearly, American base there is good for those countries economically and offer them greater security. If at end of the day, Cambodian government just says that we don't want permanent Chinese presence here, then that's different story. China should pursue a base here as long as it's in their interest to do so.
For the second question, I think you should really think about the range of different pla weapon platform and where their threats come from. It's quite strange to me that you think a base in Gulf of guinea is more important than a base around Malacca straits.