Make sure the seat is anchored well, you don't want the seat belt to be taking the load of you and the complete seat assembly together.
Also work out a way to use a shoulder belt too, even with lap belts your going to whack that non-collapsing steering column and the header panel over the windshield pretty hard if you do have an accident.
Also if you are having kids ride in the truck definitely use shoulder belts, there have been terribly severe spinal injuries to children who have only had a lap belt on, as they tend to buckle over in a crash damaging their lower spines, because they aren't tall enough to hit the dash, this is why you don't see lap belts in the back seat any more.
