Occam's Razor dictates that ordinarily the simplest solution to solving a problem, is the solution. The 4 most common points of failure on a Suburban RV furnace are the Sail Switch, Electrode/Ignitor, Control Board and Limit Switch. I'd start by first cleaning the sail switch, if that doesn't work try shorting the leads. If by shorting the leads the furnace ignites but then shortly flames out, it's likely a control board issue. You can unplug and remove the board and clean all the connectors with a fast drying contact cleaner. Otherwise you may just need a new board. Boards are notoriously finicky and especially if you've gotten water anywhere inside the furnace area from the outside ( most likely from a pressure washer or hose nozzle). The two most unlikely culprits would be the ignitor and flame sensor, but that doesn't mean the problem couldn't be in either of them.
