Congrats! And welcome to the wonderful world of "glass"
As for the P-trap, you can call Casitas 1-800 and ask for the service dept. Can't rememeber the guys name, but super cool and gets parts out to you pronto! I looked everywhere from Lowes, HD, and everyother hardware store I could think of and the didn't have a rubber p-trap. Had rubber J-traps but not P. In Denver you may have a better chance than I had in Greeley but it wasn't worth driving around any more than I had already looking for it. And Casita
was quick at shipping it out. Again, Congrats!