Our RV furnace will fire up perfectly one time, but the next time it won't. We cleaned the igniter and orface. What do

when it lights, does it run until it reaches temperature or does it shut down soon after. also, what is the make and model of the furnace

hmmm. well since it clicking, sounds like it may be an issue with either the gas valve or gas pressure.
the furnace is pretty pressure sensative, requires a good 11"wc of pressure to work correctly, it is possible, for some reason you dont have the pressure. this can be checked at most Rv service centers for a about 30mins labor and they can adjust it as needed.
next would be the gas valve. if you remove trhe outside access cover, you should see the gas valve at the front, will be inline with the gas line. should have wires going to it. i would use a test light, and first check that you are getting voltage to the gas valve when it is trying to light but failing. if voltage is present, see if you can hear or feel it click. should click open and try to light, then close, then retry again, 3 times usually.
the only other thing i can think of could be the elctrode is not set properly. should be, 3/16th inch above the burner, its possible it is too far away or too close and not sparking correctly, so worth checking that. check those thigns first and let me know...

ok.. good luck.