Go here, I've covered this pretty much in depth...
I did a good job of explaining the good and bad tech.
You have to use a two-stage regulator, they're the only safe and reliable way to go. You can get one cheap or free from junked trailers/fifth wheels/RVs. New they're serious buck$.
Hoses to connect the tank to the regulator to the gas line(s) are available for cheap through most RV catalogs and stores. DO NOT cobble up something from automotive hose.
Mount the two-stage regulator next to the tank. Then plumb the low-pressure line down the length of the bus, T-ing off where you need to hook it to an appliance.
MAKE SURE YOU HAVE A GAS SHUT-OFF AT EACH APPLIANCE !!!
The valves are cheap, around $7 each. Do NOT use water valves, use ONLY gas valves !!!
Use ONLY flare fittings and/or threaded gas pipe fittings, where applicable. Do NOT use galvy pipe, it's not gas tight.
Use ONLY copper and/or black iron pipe, with the appropriate brass/copper/black iron fittings.
Larger RV places sell adapters so you can run your RV gas system off 20 pound tanks if you wish, like if you con't want to break down the camp and move the bus just for a refill. The 20# tank sits on the ground, using a hose and adapter to your existing tank.
If you want to know how big a gas line to install, take a list of your appliances with you to a place that does propane installs and maintenance. They will have a list/chart of pipe/tube sizes for what you need, to ensure adequate gas supply to each appliance.
I salvaged a BUNCH of stuff for free from a fifth-wheel trailer:
four burner stove/oven, six gallon Suburban water heater, Suburban forced air furnace, the two-stage automatic regulator (I'll be using two 20# tanks), much of the copper and fittings.
Cost? The gas to get there and back, and helping the owner junk the rest of the trailer.