questions on enclosure design

[greenskier420 0]

I'm going to build a box for a Fi Bl 15 that needs to fit against the angle of the seats in the cargo area of my 4runner. I want it to be ported and tuned to about 33-34 htz, but i'm having trouble finding out how to tune the box with the angled back on the box. I was wondering if anybody knows of any online programs or calculators that would tell me what size the port should be in the box to get it tuned right. Thanks for any help.