Need help with badly hacked theme – Content div will not go to 100% on some page

Hello,
I have been working on this site for about two months now. The theme is a God-awful mess of bad hackjobs but they’re stuck with it. So, I’ve been tasked with, among other things, building new full width page templates. I’ve gotten the majority of the site switched over. The standard new full width template works a treat but whenever I try to incorporate these changes into the search page, 404 page or anything with a sidebar, the main container div collapses. So, all the content pushes through the bottom.

I’m currently working on the 404 page and have setup a test page using it as a standard page template (basically just so others can look at it). As you can see, the main container collapses and the content is pushed out. I have eliminated all of the bad old styles that I can, applied 100% styling to each container both in the stylesheet and within the div tags themselves (old school :)), registered a new sidebar to use to eliminate that as a possible problem and then banged my head against the keyboard allot. Nothing works.

So, I’m sure it’s something simple that I’m overlooking so I need fresh eyes to help me out. I’m going to overthink this to death, so check it out and let me know what you think.

P.S. I did NOT design this site nor is any of the major funkiness my fault ??

Test 404 page is at:
https://www.penncare.net/404-test/