vman, to legally and safely install a new permanent propane tank will COST A LOT OF MONEY, no matter how much extra storage space you have.
Posters have tried to explain that you do not need to fear running out of propane just because you'll be camping for a few weeks.
How much carrying capacity on your coach? Do you even know how to determine your carrying capacity? Trust me, its not about filling it up until there aren't any more space!
If you just load up an older coach with any old thing, you are increasing the handling difficulties, increasing the stress on your tires and increasing the chances for an accident.
Before you make the decision to start carrying around an extra 200# of propane you don't need, find out your GVWR (gross vehicle weight rating; it should be on a specifications plate in your coach somewhere) load up your coach with the fuel, propane, water, waste PEOPLE and luggage you will be traveling with and GO GET WEIGHED.
Go to a truck scale where you can have all 4 corner weighed; at a minimum you need to know the load on front vs rear axles. You need to have your load balanced and this is the only way you can figure it out.
The total weight needs to be LESS than the GVWR. Running overloaded is just flat dangerous, particularly with an older coach.
When you've done that, you can make a decision about whether you want to give up 200# of your carrying capacity for enough propane to last you a year, or whether you'd rather carry other stuff and only fill up on propane every 3 or 4 months.
Life rocks when your house rolls
Senior Chief & the Cheese Queen