I recently bought a 1.5W video transmitter.
Although with larger transmitters the range is better they are heavier and mine in particular got very hot when stationary (not in flight).
The transmitter comes in a gold/orange case which acts as a heat-sink and protective cover. Weighing in at 1.5 ounces (43 grams) for just the outer casing.
I simply unscrewed the outer casing, making sure the LED cover was retained.
This was then held in place with a tiny drop of Medium CA (super-glue).
I then bought one of these. ( a computer RAM heat-sink 35mm by 35mm by 14mm , as long as its something which can be cut easily - avoid cutting through a fin.)
By cutting this using a table-top jigsaw i cut it into strips that suited the transmitters back. I then glued these on (thermal compound).
It now looks like thisThe total weight save is 1 ounce (28grams) and it stays much cooler. Plus with the blue makes it look snazzy . If your worried about voiding any sort of warranty then i wouldn't recommend this but it much better suits my H copter as there is less air flow then my old aeroplane it was mounted on.
Total cost £2.50 or around $4 for modifications
Hope this helps - Ed - Doctor3