...I even question the need of a PVB in my case...
I ASSUME that by "PVB" you mean ANY form of backflow. When it comes to irrigation, the only case where you don't NEED backflow protection is when the source for irrigation and drinking water are not the same. Otherwise, if there is a physical connection between a drinking water source and irrigation system, some sort of backflow IS NEEDED. I understand it seems impossible for any sort of contamination to make it's way from the lawn back to the drinking water, and it is something that is UNLIKELY to happen... but then again, it is UNLIKELY that you will be in a car accident on your way home. That doesn't preclude the need to use a seatbelt. And if you don't understand how, then you're going to have to just trust me when I say that under the right conditions... it is possible.
Now if by "PVB" you are thinking you can use some alternate form of backflow protection, there are alternatives that can be installed just about anywhere, namely a Double Check Backflow preventer. However, this type of backflow is only sutible if nothing else is being added to the irrigation water (such as fertigation). Additionally, you have to check local plumbing codes to determine if they are even allowed. Some places they are, some places they are not. Double Check backflow preventers are not as safe as PVB. Think of PVB as that seatbelt with a shoulder harness. A double check could then be compared as a seatbelt with only a lap belt (while the RPZ would be the model with air bags with side-impact protection).