I am currently using WahooHD housing with Sony CLM-V55 monitor, and I am more than satisfied. Whole case is made from aluminium and you can choose what bulkhead you need, depending on housing manufacturer. I choose this one because I needed housing that can go over 100+ meters, and WahooHD depth rating is 450ft/140m... I am using it with Aquatica housing and Canon setup.
As you already said for UW video, external monitor is game changer... It is way more easier to record...