I cannot comment on the 20 pounder. But this might help you some. I have a 15 pounder, fairly long bottle especially if you have those fancy curved handles. Mine fits easily with a hard or soft top. It's fairly heavy when full, around 33 pounds I think. Just got mine filled today and it cost me $25 to have it filled, but the price varys quite a bit in my experience. I get mine filled by a dude that does fire extinguishers, and he will pick it up from me and bring it back, usually the next day or the same day. On the jeep the bottle just fits. If you look at this pic, the bottle might have 3 inches to spare underneath it where it is hung. But it is put in this position cause it didn't put the tank bracket in a bind. But there are lots of different tank mounts. With a different one I could probably push it down some. FWIW, I LOVE my CO2 tank. it is as handy as running water in a house.