The allowable location)s) of the fuel pump depends on the characteristics of the particular fuel pump, e.g. it's lift and pressure characteristics. However, fuel pumps generally work much better at creating pressure, than drawing against vacuum or load. Therefore, you would ordinarily want to locate the fuel pump at, or near the fuel source (the tank). This means usually under the van, mounted to a chassis/frame component. Also make sure the orientation is correct. Some fuel pumps must be mounted in a particular orientation horizontally/vertically in order to have any longevity.
Wiring the positive power lead on the pump to the ignition post on the TM ignition switch is ordinary. If the TM frame has good continuity with the van chassis, then you can also use the van chassis as your fuel pump ground. No worry about draining the van battery.