[asid61]

35-40lbs sounds a tad low, especially with bumpers. and a lack of lightening holes in the sheet metal. 40-45 without bumpers would be my guess.
As Paul said, you can get accurate weight estimates by adding materials to parts and using the listed weights online for COTS parts. This is a major feature of CAD that can be used to excellent effect.

As Joe said, you will experience strength issues with those center members. Your superstructure should be designed to support your chassis if you're planning on keeping those cutouts.