Two 20# BBQ tanks. One is currently full(ish) and sitting on the ground next to the bus. The other is empty and needs to be filled. they will be mounted under the bus with an auto changeover valve. The front LP tanks will only run my 30" gas range and the water heater.
Also will put two 20# BBQ tanks at the rear of the bus next to the water heater that we will use to heat the fluid for the hydronic heat exchanger. It will also allow us to swap out the tanks, if needed either front to back or vice versa. The heater tanks will also have an auto changeover as well. Because LP (especially for the heater) always runs out in the middle of the night, necessitating that "someone" get up, get dressed and go out in the rain/sleet/snow to swap the tanks.
Our neighbours at the last park we stayed at, swapped 30# tanks every three days on an RV furnace. It ran all the time. Some RV furnaces suck LP like there's no tomorrow. We had an older (1980's) Suburban in the Class C and it was pretty good on LP. We normally used electric heaters and ran the furnace as a backup (if the inside temps dropped to 60, the furnace would kick on... the electric heater woulds keep the furnace from cycling on too soon when it was single digits outside). With the bus, we will have an electric heater in the front of the bus (living area) and add a "hott rod"
to the tank that heats the fluid for the heat exchanger. That way, we can use the AC included in the site rental OR use LP if the power is out or while wallydocking OR use LP if the LP is cheaper than the metered electric.
Why 20# BBQ tanks... Because it hard to do a tank swap with a 30lb tank! We can swap out a BBQ almost anywhere (and have). While refilling a tank is cheaper (not always), LP fill stations are not open all the time... like weekends and holidays, you know, the times when you run out of LP and have no backup because you forgot the other tank ran out... and a winter storm is heading in. Not that we have ever had that happen.