I've been thinking about a front bike rack because putting the bikes on the back of the truck means that even without the trailer, I still have to unload the bikes in order to get clear access to the cargo area.
And I don't want to mount the bikes to the trailer -- we often drop the trailer at the campsite and then take the bikes on the truck to go mountain biking elsewhere.
Just to be clear, at my age "mountain biking" no longer means "screaming adrenaline death defying single track adventure." It now means "gently rolling along a wide dirt road looking at the scenery." ;)