Problems with RV systems can be very frustrating at times, but hopefully you will find the cause soon and will be able to focus on travelling and camping instead.
You said that the furnace control board replacement enabled the furnace to work for about a day.......which suggests to me the basic furnace control systems were working (at least for that long). Possibly while installing the new board you temporarily moved a loose or intermittent connection/wire.
I was also wondering if you are having any operational issues with other propane appliances? Weak flame on stove; fridge or hot water heater not firing up properly? It is not uncommon for the propane regulator near the tank, to leak or fail to regulate gas pressure properly.
Long & Winding road had some valid suggestions and questions that are important to respond to for the forum to try to help you. Providing as much information about what is happening (or not) during the failure time, makes diagnosing easier for the forum. (i.e., the blower ran Ok but did it shut down after 30 seconds or so?; did you smell gas at all during the start sequence?; any sound of spark attempts? You may find a mobile tech to be a good solution if getting into a Dealer is not in your time frame requirement.
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