Installing a Propane Furnace in My Garage

I have a 90,000 btu furnace that i would like to install in my garage. I live in the city so there’s an ordinance against having propane tanks in town. However, a 100 lb propane tank is still considered a portable tank. I would like to run the furnace on the 100 lb bottle, but don’t know what type of regulator to get for my bottle. I tried a 30 lb bottle with a barbecue regulator and that just didn’t work. I was told there wasn’t enough volume in a 30 lb bottle but a 100 lb should work. I don’t really want to fork out the cash to get the bottle updated and filled until I find out what kind of regulator i need and if the 100 lb bottle will have enough volume. My garage is very small, about 15 X 25. not to be used to maintain the garage at a certain temp, just to heat it up when i want to work in there, and shut it off when im not working in there. Any help would be greatly appreciated!  Thanks Terry.