Issues with insurance are more relevant to driving your own vehicle. You need business insurance if you are driving for work. Comes with some policies, is extra on others, just check if you are covered or not.
Personally I always use a Service vehicle, the rates of duty mileage are insufficient, even with tax relief. Issue there is what happens if something happens that you might need to claim for yourself (vehicle fault causing accident and injury to yourself for example) and the support with a subsequent claim that you might get. Always best to ensure that you have some sort of legal cover for your subsequent fight with MoD, but there are plenty of 'where there's blame, there's a claim' lawyers out there.
As for the allowances system, someone needs to sort out the barking situation asap. The only equal way of treating singlies and pads is for there to be no charges when deployed away from parent Unit. It is not right that singlies continue to pay food charges while others do not. If I go away from home I am not eating food from my fridge; hence I am not spending money on it. It seems logical that we should all be treated the same way.
This is really not rocket science is it?