Suburban Furnace intermittently doesn't light

I have an issue that is confusing with my Suburban SF (20-35?) furnace. It was installed I believe in 1999. We have a 1999 5th wheel. We are in North Dakota and have been using the poor furnace all winter. It has been working great all winter but suddenly it has started to periodically fail to ignite.

When it does not light here is what happens:
The blower comes on.
You hear clicking from the ignition.
You smell propane from it not lighting.
The blower will continue to blow cold air.

If this happens in the might when we get up you can smell propane through the camper (I am guessing from repeatedly trying to ignite?)

Sometimes it will fail to light when the heater is turned on. other times it will work just fine for hours, then suddenly fail.

I replaced the propane regulator hoping it was just low pressure. That did not fix it.

Checked for propane leaks and found none.

What could be failing if it is getting spark and propane?

Any help would be much appreciated! It is hard and extremely expensive to get help out here. We live in our camper so we will need this fixed before next winter. I am so grateful that it didn't start doing this until after the -50 weather!!

Thanks!
Nikki