In our previous van, a 2010 model we had a Sanyo microwave that failed after 14 months. Swift said that although the van had a three year warranty, the microwave was only warranted for twelve months. Having had loads of hassle with Swift over the years I really didnt fancy another argument and asked would they supply one if I paid for it. They said they couldnt supply one, I would have to source my own. When I tried to do this, I found that the model in question had been discontinued as they had had repeated fails on them. May or may not be the same model, im sure they will have had stocks.
Anyway, the original model had no cooling grills in either its top or sides, cant remember which. It appears these are the type recommended to be fitted in confined spaces. On all the ones that we found would fit, the instructions were very clear that it was NOT to be fitted without a certain airspace around it and a flow of air to it. We had a hell of a job trying to find one that didnt specify it was unsuitable. I was concerned that had we had a fire or problem the insurance would have turned us down for fitting a microwave of this type. Eventually we had the second type anyway, bought from Asda for £60 and never had a problem with it.
One point of note. Our van had a metal plate in the microwave space that was designed for the front feet of the microwave to fit into, thus holding it safely when travelling. This also limited our choice of model.
Good Luck!