I'd probably use a 331 series. A 341 if you have the realestate and want a massive latch.
As well, I'd spec an R series for the lock considering the application. In the southwest I wouldn't worry about getting one in 304 stainless, the zinc plated steel units would be fine.
So you're thinking something along these lines? http://www.amazon.com/DE-STA-CO-341-R-Action-Threaded-U-Bolt/dp/B0006NC6AI/ref=pd_sbs_indust_1
They provide some dimensions but they don't seem to agree with each other in different pictures, but even if it has the larger set of dimensions I should have just enough room to fit it.
I almost forgot I had autocad. I am ashamed. I will have a few additions sometime
Too busy working on the pimp mobile haha, post some stuff up when you get a chance.