I just finished checking mine the same way, and the TEE is extended way up. It would take a very full/overfull tank to slosh out through there, in my estimation. I only saw the one vertical ABS pipe, though.
My propane detector, however, had no backing blocks! Just screwed into the panel.
2009 Tacoma Crew Cab, TRD 4WD
2007 Tundra Double Cab TRD 4WD
2014 Escape 19
2007 Norwegian Elkhound "Baxter"