If you are only talking about towing a few hundred miles a year, then a gas vehicle will save a lot of money on cost to buy it, insure it, change the oil, and other maintenance items.
You can also look at 2011 and later Ecoboosts, but as you said Employee pricing is pretty good. The new aluminum truck beds should have a great resale value, but most Ford dealers are not going to offer A plan pricing on the 15 trucks until they run out of 14's.
I would be suggesting a low mile truck, such as the F-250 with a V10 or 5.4L v8. Both will offer plenty of power, you rarely need to drive it, so MPG is not a issue. It will carry all the bikes that you need in the back, so a shell will keep it all secure.
You can also look at gas Excursions. They are wider and longer, offer up to 8 seating. Look for a low mileage one, if you can find it. Do not get a 6 liter diesel, they are cheap for a reason that has been well discussed many times before.
Check the towing capacity on the Flex too. I think you can get the same 3.5L Ecoboost, and should have seating for 8.
Fred.