In conjunction with Camper Bob's suggestion, I would add that in the event your bottom is covered/sealed, look for two white tubes (about an inch apart from each other) extending downward underneath your trailer. See if those tubes are plugged (eg, dirt and/or insects).
2004 Suburban 2500 LT 8.1L/4.10/4x4
Putnam XDR Class V, Equalizer 1400#
2006 Jayco Eagle 264BHS
Iota DLS-55, Progressive Industries EMS-HW30C, Trimetric TM-2025