DISCLAIMER: This is based on my experience. Your mileage may vary.

The water heater pilot light on our 19' 5ver wouldn't light, unless you held a lighter under the thermocouple.  Even then it was not certain the main burner would light. It turns out that the fix is easy enough and only $15 for a new pilot light and thermocouple from Amz.  Atwood (91603 Jade Pilot Water Heater Assembly https://amzn.to/2DBykiM ) Once I had the new part in hand I removed the old one, which was easy enough.  You will need three wrenches to remove and replace the part. 

The tiny sheet metal screw that holds the pilot light down is under the pilot light and takes a 1/4" wrench. The Thermocouple nut in the regulator is a 3/8" and the pilot light supply  line is a 7/16". Always use real wrenches as a crescent wrench will possibly strip the soft brass fittings. Once the old one is off, you need to check whether the sheet metal screw that holds the pilot light down will screw into the new fitting. I've heard that it wouldn't and that was the case for me. I ended up using what my harbor fright drill index said was a 5/32" bit to drill it out enough to allow the sheet metal screw to start and still have enough meat to grab and hold the pilot light bracket.  If you find you need to drill out the hole, now is the time to do it while you can hold it upside down on the work table and make an easy job of it. Test the screw before you go any further. 

Now starting with the thermocouple line, very very carefully shape it to fit into the regulator, and while this can go easy, i had to fight with mine for quite a while to get the brass fitting to engage BY HAND a few turns. Because you are screwing into aluminum you must be very careful not to cross-thread the brass fitting. It requires much wriggling and angle adjustment to get it right. Never use the wrench at this point. When the brass is engaged safely, go ahead and tighten it about halfway, leaving things a little loose for adjustment.   Once you easily engage the thermocouple line you can do the same with the pilot light line using the same cautions. Again don't tighten them all the way down. 

Next carefully shaping the lines to allow the pilot light to mount in the burner hole, use the sheet metal screw to mount and hold that assembly.  Tighten snug but don't strong-arm it, because you have removed some ot the metal for the screw to bite into. If you strip this screw it's time for a tiny nut and bolt.

Lastly go back and check that all the lines are clear and leading smoothly to the regulator. Now do the final tightening of the brass fittings. Be careful not to over-tighten the fittings. None of  them carry pressure. The thermocouple line is sealed at the end and apparently expands once it's heated enough. The pilot light line goes to an open burner and so has no reason to leak under pressure.

If all goes well you should see results like these:

With any luck you can finish this job in 15 min like some did, but even if you run into problems it's not too hard and can be done while sitting on an upside-down bucket.

An Addendum:

I have  noted some comments on using pipe dope/ teflon tape on the brass into aluminum fittings. Because these are under no pressure there aren't any worries about leaks, however if you had some Propane correct pipe dope handy, it might act as never-seize and help if you should have to change the fittings out in the future.  Mine looked to be the original 22 year old fittings so I expect these to not need a change out anytime soon.