"The other option would be to look for a housing for an SLR with a dome port that can take a reasonably long zoom"
I've been looking for housings for film SLR's. I figured that most serious UW photographers (and a lot of gear hounds) would have moved to digital. I haven't been able to find housings for, say, N90 or F100 cameras. I don't know if they were remachined for digital bodies or what happened.
Digital for UW makes a lot of sense. Use a big card and you don't have to open all day. Opening a Nikonos on a boat to change film is (a) a chance to get dirt/water into the camera and (b) a chance to get a leaky seal. Making it so you only have to open the camera at night, in your hotel or dive boat. would be an advantage.
On the other hand, Nikonos cameras are so cheap that if I get back into it, I'll get a couple of extra bodies. Just swap out the body and strobe after each dive.
Flooding a digital camera and lens (likely a couple of thousand bucks) is not a very attractive prospect. Flooding a $200 Nikonos, not so bad. There is flood insurance.
I bring this aside up for a reason--dive cameras are mostly designed for diving. Not rolling around in the waves. Getting pounded by a big wave increases the risk of a small or large leak. At the surface you don't have hundreds of punds of pressure on your dome to help keep the seals tight.
Standard practice is to get in the water and have someone hand you your camera. You don't jump in with it. Being on the surface with waves is inviting a leak.