In your dispatch there is a step up from the load bay to the cab, this is a structural cross-member. If you have your tank strapped to the floor against that you will be fine, as there is no way that tank will come forward in the event of an accident.
As for your kit. Tank-pump-di-hose reel. Mount the pump low, and use as little hose and connectors as possible between tank and pump, this will minimize any airlock problems.