Could someone help me with the dimensions for a box. I'm wanting to go 1.8^3 @ 30hz. This will be for a single 12" rl-p, and will be going in the back of a tahoe, so room isnt really a problem.

Just use an enclosure calculator

www.the12volt.com/boxcalcs.asp

( should be right)

click on link in sig

That works too

Well I had someone at caraudio.com come up with a design for me, one was for 1.65^ft3 @28hz and the other was 2.0^ft3 @34hz, but I forget my amp doesn't have a subsonic filter, and I was going to buy an inline 30hz filter, so which of these boxes doyou think would be better for my amp and sub?

use the 2 ft^3 tuned to 34Hz, just don't play tones below 25Hz.