In another thread (single propane tank), tampajohn describes
his remedy for the horizontal tanks. Maybe you would consider what he is doing.
Personally, I have found my tanks to last at least 3 weeks of summer camping, cooking on my stove (outside) every day. Winter would reduce length of time between refills, but I think removing tanks to fill is going to take effort either way (horizontal or vertical tanks), and it is more convenient for them to be under the slide than to be messing with moving them around, running extra hose, etc. Refill every three weeks is not too often to remove the tanks, I think. Just my opinion, though.