For an IB setup, having any holes where air can pass between the trunk and cabin is a big no no. You want the two spaces completely separated.
I wouldn't use either of the JBL amps. The 300.1 will be making 75w @ 8ohms and the 600.1 will be making 150w @ 8ohms. Your best option is to buy a 2ch amp and run it in bridged mode. Mono amps just won't make a lot of power at 8ohms.
How about this
US Acoustics USX-2150 which will put 300w into an 8ohm bridged load ($150 shipped).
