After a couple of days of research, I think I've sorted out issue with furnace. But I don't know how to access the problem area.
According to the Suburban Service and Training Manual for my model (Suburban SF-42), the control board first checks to see if sail switch is open (i.e., not getting air) before blower starts. If sail switch is stuck closed (i.e., thinks it's getting air when it's not), the blower won't start. I had connected a voltmeter to the only two wires I could access enough to disconnect and result was they were getting 12 Volts when thermostat was set to "furnace" and above room temp and zero Volts otherwise. Initially thought those wires went to motor. But after studying wiring diagrams and viewing pics of motor, I'm now pretty sure they go to the sail switch.
All that plus two clicks I hear 30 seconds apart when the fan ought to start blowing but doesn't and what the S&T Manual says under "Sequence of Operation" for my model make me think a stuck or completely malfunctioning sail switch is the likely culprit. Unfortunately, I can't access or even see the sail switch. Nor can I access the terminals of either of the wires that I now suspect go to the motor to test it directly unless I cut them. And after A LOT of googling, I STILL can't find anything that explains what I have to do to remove some or all of the furnace so I can get to the sail switch or motor wires.
If anyone knows or can point me to something that explains how to access the sail switch OR the motor wires in a Heartland Bighorn 3670rl with a Suburban SF-42 furnace, would be VERY grateful. Temps drop to 24 tomorrow night for two nights and then a few days after we're supposed to have a four-day-straight spell of nights in the mid-20s. So really need to get this fixed pronto or else figure out a way to keep guts of trailer warm enough so no water lines are damaged from below freezing nights till I sort it out. Also, as interesting as it all is, need to get back to my paying job really soon, lol.
EDIT: Pretty sure sail switch is behind part of casing circled in green in pic below.