Depends on whether you are willing to wait for the compressor to replenish the tank. Had a friend who had a small pancake compressor which he used to run his impact - would get about 2 licks on the trigger and then would have to wait while the tank filled again. Tank cost goes up dramatically with capacity...that's why for on board use I'd suggest looking into two smaller tanks to give you capacity instead of one huge tank. I would think they would be a whole lot easier to mount, too - those big air cylinders really don't "just fit" anywhere unless maybe you have a real shallow toolbox you could get one under?

 

This is the system I'll be buying for my boat. It is compact and you could add storage to it if needed, although they come in different sized and cfm and storage configurations. Sometimes it is easier to buy a set-up that is all done and you just install it. Might end up cheaper, too.

 

I used 3 gallons and didn't seem to have enough air but my air tool were from the 40s-50s

 

My thoughts-
Using the 2000 psi tank is adding a lot of weight but you won't gain any pressure over what your compressor can push.
If you used a removable air pig tank, you could use it to seat beads, take air to another location/vehicle, and it weighs a lot less than the 2k tank, but it should hold what most 12v pumps can deliver.
However, if you were going to use the 2k tank anyway, why not just put a new 2k in it and use a regulator? I know you couldn't refill it without an exchange, but you could put air, nitrogen, whatever you want in there.
You could make anything work, but I'm thinking you'd have a lot less plumbing and pieces with a 2k bottle and a regulator. By the time you add plumbing, brackets, wiring, etc, it's going to add up.

 

I made mine for the cost of an air chuck and pipe dope

If he can get a 2k tank for cheap or free at least he won't have to worry about it getting dented by a rock kicked up by the tires

If it's going to be bought for a lot though I'd go for a different tank

Cheaper usually isn't better but it's better than not having anything