I 100% agree with diesel for heating. The Eberspacher/Webasto units are frugal on fuel and generally work dependably for a long time.
In my experience, gas is a better cooking solution unless there is another reason that you need a huge electrical system. Unless you have a truck bloated to the gills with convenience tech, it is likely that you'll only need a fairly modest battery/solar set-up, which will struggle with electric cooking. Most of the world uses exchangeable gas bottles for cooking, so as long as you do a bit of planning with adapter hoses, you'll have little difficulty finding gas anywhere in the world.
Will Hayward supply a bottle adapter system which will let you connect pretty much any gas bottle you'll find globally, to a regulator which is static. I've used the system to adapt Italian, French and American bottles with no difficulty at all.
I would avoid gas for heating, only because of the rate that you'll get through it. It works ok if you have a huge integrated tank, but these are very difficult to fill up outside of Europe or USA. With small exchange bottles, you'll be swapping them out every week or in cold climates; no problem for motorhomes used for short trips, but it'll get old pretty quick if you're full-timing. Conversely for cooking, I got about 6 months out of UK 13kg propane bottles, including lots of roasts in the oven.
