I have the yakima bettyjo which is meant for truck beds - even if you have a topper. It costs about $120 and does a fine job. My brother has thule locks on a 2 x 4 and I like it much better than my bettyjo. It allows for a lot of vertical space which is nice if you have a topper and taller bikes. I think the set up cost my brother $50. My yakima isn't able to handle triathlon bikes very well because of the aerobars, but the 2 x 4 works wonderfully.