thanks for confirming. you will need 4 wires from the thermostat to the air handler and two to the outside. the heat system should already have accomodation for turning on the heat strip and fan in heat mode. it's possible that this is a single speed motor because it was heat only. in some cases, depending on the age of the mobile home, the blower may be inadequate to deliver the cfm necessary for cooling. you may have already researched and addressed this, but you should be able to confirm with a distributor for the brand.
if it is a single speed motor, you will need a spdt (single pole / double throw) relay with a 24 volt coil. you may also need to change the transformer. a heat only setup could have a 20 VA transformer, which can handle up to about .8 - .9 amps. you will be adding a fan relay and contactor to the load, so i would suggest a 40 VA. there are a few possible configurations for the existing heat control circuit. you may have a contactor or sequencer. you may have a relay for heat and only a thermal fan switch. you should be able to incorporate the existing controls, but you may be better off using a fan relay and sequencer.
if you upload a shot of the control panel and a closer view of the connections, we should be able to help you with a circuit design. also note the va rating of the transformer.