Last year shortly after taking delivery I decided to completely gut the over-cab area. Our needs were never going to include using the upper bed, but we really needed extra storage for bulky stuff. I regret not weighing the materials removed, but I would guess the mattress, console, etc. probably was 100 lbs.
The materials I used for the assembly probably weighed the same or a little less than 100lbs. The two center sections are sliding trays that pull out 24" to allow easy access to the far front area (the cabinet is 38" deep).
I used double faced foam tape under the front of the frame rather than permanent attachment with screws - meaning I could remove the whole assembly and not have any holes in the coach. The assembly has never moved a fraction in six thousand + miles
We use the center cabinets for personal stuff, meds, vitamins, etc. all stuff that we use several times a day each. The side cabinets are filled with extra bedding, extra clothing (I write this from Homestead Fl. and in the last month we have been thru 3 seasons Va.- Florida - a lot of clothes), space heater, other light things. I doubt the total cargo weighs 200 lbs.
Total cost was under $200, the most expensive parts were the plastic windows that cost 40 and custom mixed stain for 35.
For us it is a win-win project.