i am doing a 4th order in my grand cherokee and was wondering what would be a good sealed chamber and ported chamber.

Equipment i have right now:

2 18" DC lvl5's

2 Sundown 4500d's

1 300 amp powermasters alt

8 3100's

You mean a bandpass, not just a 4th order. Either way, don't listen to anyone with a rule of thumb as it will only give you results that are worse than with a simple 4th order ported.

Level5s in a 4th order BP? That just sounds like failure.

Level5s are geared toward ported enclosures only.

Will it work? yes.. will be it wise? Hell no! Terrible effectiveness.