A U2 song? No, sorry, sorry.
Never minding all the discussion, all anybody really wants is you to find out why you RV won't start reliably.
An issue seems to be that Ford built starting systems for coaches like yours in two configurations and considering that you seem to be in unfamiliar waters here, we'd prefer not to steer you wrong. Well, I wouldn't.
If the diagram linked to is valid for your coach than you would not have a big bolty looking relay like I pictured and would instead have a very much smaller 20 amps style relay in your fuse box along with some other relays just like it. If that be the case you can swap it with another relay like the horn or something as a very simple way to find out of it is good. They don't fail very often, it's usually something else.
subford might have a diagram of the fusebox to help you locate the relay, he's a goldmine of such information. I have diagrams but only for the F-series trucks, they may be the same but I don't in fact know that.
I guess you know a repair shop could probably suss out the problem in short order. A couple of problems with that though. First, you would miss out on no learning a bit about your coach and maybe engines in general. And second, there tend to be two kinds of shops. First will find out what is wrong, however long it takes. The second will say "Oh it's your starter" or battery, or something. Then they replace that component and if they guessed right everybody's happy. If they guess wrong, they charge you for whatever they did and start figuring out how to charge you for now finding out what the problem actually is. From outside it can be VERY hard to tell these shops apart. And even inside the shop there can be both types of employees. It's a gamble. But the more you learn about such systems the less shop type #2 can BS you into to overpaying for their lack of competence.
So I feel that if you have the time and energy to continue pursuing this issue on your own it might be worth your while.