1984 P30 454 Shredding Alternator Belt

I have a 1985 p 30 pace arrow with the exact same problem. Turns out it was the pulleys themselves. Check the grooves of your pulleys, if they aren't absolutely smoothe and shiny, that IS your problem. Over the years and period of sitting, they tended to rust and when driven, any roughness inside the pulley groove would shred the belts. I kept loosing alternator belts every 100 miles or so. I'd notice the volt gauge drop and had to put the belt back on. So to not have to worry about the pulleys ever again, I went to summit and bought all new aluminum pulleys. But if you do MAKE SURE YOU GET STOCK SIZE PULLEYS!!! They sell a lot of underdrive pulleys for hot rods to slow the rotation of everything for more power, not good for an RV to have a slower rotating waterpump. I also removed the air pump since the pulley was pretty nasty too. You have to remove the entire pump, not just the pulley as the pump itself sticks out too far and will interfere with the belt. The only pulley I didn't replace was the power steering pump for 2 reasons. One being that I haven't had a problem with that belt, and the other being it's pressed on, and it's a pain to remove unless you pull the pump out which is a messy job by itself. So ill do it later if it becomes a problem

Here's my interior:



With the lid off:


I took the whole cover off to give me more room to work:


Here's the alternator. You can kinda see the roughness in the groove of the old one. I decided to upgrade while I was there, to a 100 amp alternator. The steel pulley it came with is junk, way too thin for the proper belt, so I got an aluminum one. BTW, that's NOT a double pulley, it's the reflection of the first pulley in the shiny chrome fan cover. Alternator was $100, the pulley was like $26:


Here's the water pump pulley. I think this one was like $40:



Here's the crank pulley. In the outer alternator belt groove doesn't look bad in the picture but this because the groove was so rusty, it's caked in rubber from all the belts it's shredded. A quick wire brush revealed how rough from rust it was. There were several manufacturers that claimed they were selling a stock sized pulley at 6.x inches diameter, which is smaller. There was only one that had a true 7 inch diameter pulley, I believe it was billet industries, I think the one by March performance was 6.X inches. IIRC this one cost like $75:



Before I was lucky to get 50 miles before loosing the belt, it's been over 1000 since i put the aluminum pulleys and the belts still look perfect and they're still nice and tight. Keep in mind after 20-50 miles or so a new belt WILL stretch a little, and will require you to re tighten it. But after that you're good to go. Hope this helps. Good luck :)

EDIT: I went back and saw the pictures of your pulleys, and they look very rusty and rough. They looked even worse then my old ones.