Just because it's a laptop doesn't mean you have to use it in an non-ergonomic configuration. My current setup is a 15"MBP mounted on a sit/stand desk at home. An external keyboard and monitor keeps both hands and eyes in the right position. I have a similar docking setup at the office. That covers 80% of my time on the machine. The other 20% (mostly at coffee shops) doesn't bother me, and I still get the benefits of mobility and freedom.
The key is to have a good sling-back chair and to keep both feet squarely buried in the sand. I find having a low table on your left-hand side helps keep the sand from sticking to the base of your beer bottle, but you can always use a paperback for that too.
In the end, I find it's more about shade than ergonomics, especially in tropical climates where you're dealing primarily with palm trees and their small cross-section. I guess your mileage may vary.
You'd be surprised at how ergonomic laptops are. I find my macbook touch-pad to be much easier on the wrists than a mouse, and the display angle adjusts to a perfect viewing position.
The real benefit is that I get to sit in the most comfortable seat in my home, be it a chair, sofa or bed.
I have to disagree with you on the ergos of a laptop. I personally find a touchpad (or any touch interface) terrible on my wrists. And a laptop monitor is far to slow to be comfortable (you have to bend your neck to look down or have your hands positioned too high).
I'm healthier and lots more productive on a desktop with a keyboard, mouse and large screen (all at the correct heights and distances).