Six year old Suburban sf-30 furnace issue

Hi all, sorry this is long but I am trying to give as much info to see if someone has any input.

I have had issues with my furnace for a while (a few years) but now I want to get it fixed so I can have confidence that it will work when I need it most. At first it went through a time when it worked most of the time but on odd occasions it wouldn't fire and go into lockout. Of course this would be in the middle of the night and we would wake up cold. I would reset the thermostat and things would seem to be fine. Then, later in the season it would happen more often and sometimes to the point where it wouldn't run at all.

I have had previous success in using compressed air to blow in the vents on the outside of trailer to "clean" it out a bit but that is not working any more. I have also had success in standing outside when it is trying to fire and block the outgoing vent hole for a moment to create back pressure and once it fires it cycles fine for a while. A while being the rest of the year in year one. In year two it would work for the rest of the current trip. Then finally in year three I could do it (block the vent hole) to get it to run to warm up the trailer but not cycle on its own. Doing this every time you want to run the furnace gets old really fast. Especially in the middle of the night.

We have now reached a point where no matter what I do it won't stay lit. It is at its worst right now. As I mentioned earlier, I used to be able to "force" it to fire but not any more with reasonable success. For a couple of weeks I have tried to get it to fire and all it does is fire for a second or two and go out. Just a few minutes ago I got it to stay lit for a few minutes (first time in a while) using the blocking the vent hole method but I noticed the electrode kept going through its sparking cycle repeatedly the whole time it was lit. I haven't noticed this before. This is new.

So, here is what I have figured out so far:

Using the compressed air method of cleaning is doing nothing anymore.

Using the blocking the vent hole method isn't working like it did before. I used to think that maybe it had some spiders or something in there so when I forced it to run this way it would just burn them off of we were good to go from there. Worked great at first but not fun in the middle of the night. Been there done that.

Yesterday I changed out the propane regulator on my trailer to see if it was a propane pressure issue-no success. No change at all. I have always smelled propane when it was trying to fire so I know the propane was there but just had to check to see if the pressure was good. I am figuring two different pressure regulators should eliminate this as a cause of the problem.

Power shouldn't be an issue as being plugged in changes nothing.

Since the electrode was continually sparking today, I am thinking this is the possible culprit. Would the electrode make it difficult to fire or burn for a second or two and go out? Not sure.

So, with this info, does anyone have any ideas of what else it could be other than the electrode. My only guesses are electrode and possibly the board. Not much else I guess if power and propane are good.


P.S.
And hey!! This is a special shout out to the gut that thought it was a good idea to design this thing so you can't do a single thing to it without completely pulling it out of the trailer. Thanks for that. How about an access door? What are we talking here? Ten bucks?