it sucks doing things twice. if your going to bag it so soon, why not wait till then to tub the front?
or- plan ahead, take a wild guess what wheels and tires your kid will want in a few months, to a year (because kids never change their minds, right?) and plan out how low your truck will be and tub it to clear the tires after its bagged?
Here is what I did on my truck. Worked pretty well. I didnt bent the tube to fit the fender or anything. Just have the back and front bolts in it. On my first build I did this and had no problems with it. Just ran the straight box tube. I used 1 1/4" x 1 1/4" box tube.
Now here is what its looking like.