[Jeffy]

We have welded our chassis all of our years as a team. For a while our rookie year we were going to use the kit chassis, so we bolted it together, welded, then removed all the bolts. I don't remember the specific weight of the bolts and supports, but it was well over 5 lbs. We ran into trouble with the kit frame warping during the welding, so we made our own, and have done so every year so far.
If you are trying to decide what to do, I would definitely weld to save some weight. The next best option (imho) are aluminum rivets. I don't know enough about them or have enough experience to give a big recomendation, but I have seen them work very well.