I have to say don't. I have an oven and yes it's very nice as a talking point and when the Propex thinger wasn't working it was a reasonable heater but I hardly ever use it for cooking and it takes a huge amount of space.
If you are insistant then your best bet would be to move the fridge over into the cupboard next to it (given that your fridge is under your existing cooking facility) and mount the said oven traditionally under the cooker. If you are mounting it anywhere else bear in mind it will contain flames so will be quite warm on all sides and will need heat resistant insulation if you don't want to damage anything, it burns a long time so ventilation is very important and you will need to take hot spillable things out of it so don't put it somewhere akward to reach.
Euan
Economic migrant, cultural extremist and religious bigot.