y-knot

Get off the cash, and go by yourself a nice tank. The people that sell Quick-Air compressors have one or two that are very reasonable. I got there 8gal(I'd have to look it up for sure) and it comes powder coated black, has mounting brackets built in, a drain, pressure release valve, and several 3/8 welded bungs to tie into it. The price is less then 70 bones and there isn't any good reason not to use it.
When you do get around to mounting your air tank (or fence post) find a spot that affords some protection, yet doesn't make getting to it an all weekend affair.
Yell those noisy horns draw alot of air, but your tank should be at 125psi, and the noise horns are regulated to 20-30psi, so your air needs are not super natural.