I replaced my old TV several years ago with a Samsung 32" LED TV. Don't remember the weight, but not very heavy. The new TV is quite a bit wider than the old one. But they are so thin, mounting them outside the cabinet is no problem. Easiest way is to just install a piece of plywood in the cabinet opening and get a wall mount to attach the TV to the plywood. I went a bit overboard on mine, but you can see how well the thin TVs mount outside the cabinet.
Before
The opening
Cabinet insert I made
Insert installed
Complete
I did put a narrow shelf under it for additional support and use velcro strips (not visible in this pic) to secure it while traveling. The velcro strips are attached behind the TV and I can pull them out and stretch them across the TV.