For those of you suffering from the notorious Norcold N300/N300.3 "pilot won't stay lit issue," I thought I would pass on what I learned, since ALL of the websites and forums I searched on did not have the answer. After spending numerous hours troubleshooting, researching, replacing parts and finally tracing and fixing the problem, I hope I can help someone else and save you time and money. If you're finding yourself here, you're probably experiencing the same problem, that once you release the safety valve button, the pilot light goes out, making it impossible to run on propane, which is why you want a fridge in the first place.
While troubleshooting this issue (after hours of online research), I discovered that by doing the interrupter bypass (remove the blue and red wires from interrupter and connect a jumper across both terminals) the pilot would stay lit. That enabled me to test the thermocouple output (unscrew the TC from safety valve, put red test lead on tip of TC and black to ground). It turned out mine was 24mv and the TC test said to discard if it's below 25mv, which was marginal. I didn't think that was it, but decided to go ahead and replace the following components: the thermocouple, safety valve (which I damaged a specialty washer disassembling), interrupter (which I didn't think was it, but for $10 why not), and while I was at it, the interrupter wire kit (red/blue wires btw interrupter and selector switch which the mfg says are faulty and need to be upgraded). These 4 parts cost me a total of $82 on eBay.
While waiting for these parts to show up in the mail, I got a response from a YouTuber I had contacted (see "Norcold N300.3 Diagnostics for Winnebago Rialta HD") who had a similar issue and told me that in his case, the problem was the selector switch. Well, after installing the other 4 parts I had already ordered, the pilot would still not stay lit, so I decided to try the selector switch. The local dealer wanted $150 (plus 8.02% tax in my area) so again I looked on eBay and found the part for $52 shipped. Today I installed the selector switch and now my pilot stays lit! Many thanks to Rialta99 on YouTube. Below are the Norcold part numbers. Good luck!
Selector Switch 619168
Thermocouple 619154
Safety valve 622746001
Interrupter 621737
Wire upgrade 628119
