Just make sure the heater can fit a 1" line. You will have to upgrade to vinyl tubing.
an inline heater will reduce the flow output. It may be better to split the output flow with a true wye fitting and some barbs, have one side enter the tank and one side go to the heater. If you can find two wyes, you can split the flow, go through the heater and merge back together to the tank
I wold make sure that it is on the intake sie not the output, so you don't lower the flow rate too much.