I have had a !0# tank for about 5-6 years. I am going to a 15# alum tank next time I trade in the empty. The AirGas place i get it charges about the same for 10#, 15#, or 20#'s. I strap the tank to the bulkhead between the seats and just behind on my CJ8. The 15# tank is the same diameter but taller. Assuming you are streetable, If you go to Moab for a week and must air up after every trail ride when you hit pavement, a 10# tank (i've found) is marginal. The bigger the tires the worse it is. Bias ply tires fill up faster, and look firmer in the sidewalls than the same size tire in radial. I used to go up to 25 lbs. in my 36-12.5 Swamper radials to hit the street. With the bias ply 37-13.5's IROC'S I find I only have to go up to about 18-20 lbs. to be streetable. A full charge of CO2 in my 10# tank weighs 28.5 lbs. An exhausted tank weighs 18.5 lbs. Hmmm.
Get the amount of tank you need. Form follows function. et al.
regards, as always, jefe