shower will not drain

we love our PC and used it lots until......shower stopped draining.....after plunging, baking soda and vinegar, a really small "snake" and yes a chemical drain cleaner (ouch)   still plugged.  I cannot figure out how to access the plumbing from beneath the rig.  Sealed unit it looks like.  Have repaired leaks and changed out faucets and shower head but this sure has me puzzled.  Holding tanks have been drained and cleaned.  However my two thoughts continue to be 1) blocked trap 2) blocked outlet to the gray water tank.   ANY suggestions are greatly appreciated.  Our baby is a 2007, 29' rig with that wonderful green paint scheme.
Susan

Change your profile, it shows you have a 2350.
What model do you have?
Most of the shower drain directly into the gray water tank. Crawl underneath the RV at the location of shower and wee if any  line is involved.
remove plate on drain and look in drain.

Did you get anything out when you drained the Grey tank?  What do the sensors on the Grey tank show.. Full or empty?

If full, it sounds like your Grey tank drain valve didn't open.   That's the only thing in theory that would block the tank outlet.

I don't know if the 2007's came with electric operated drain valves or manual operated valves.  In either case, make sure something didn't come loose and that the valve is actually opening.

It’s too bad that Phoenix doesn’t make the plumbing diagrams available online or include them in a manual.

If you have a 29’ with the shower stall on the passenger side maybe the drain line runs under the floor and across to the sink drains? If it’s level that could be what caused it to become blocked. Perhaps you just need a longer snake.

The 29' series has the shower on the passenger side and uses the larger capacity tank (also on passenger side) for Grey water waste.  Thus, if anything, the sink would be a separate line to the tank. That maybe connects to the shower drain just before it empties into the Grey waste tank.