Hello Alan,
Lets take your points one at a time,
Is there space in your caravan for an oven to be fitted, well that depends on the type of oven you choose and if the manufactures instructions allow it to be fitted in the available space.
In general gas installation is not a DIY job, unless the fitter is competent and works to the gas safety regulations. A caravan oven is an LPG appliance and as such the fitter must be fully conversant with the LPG provisions and testing.
The manufacturer will specify ventilation for the appliance. The instructions will indicate if this needs to be external or not.
Most caravan dealers with service centres should have the skills necessary to do the job.