I know this isn't for everyone, but I've been driving for 30 years and needed the spare tire exactly once.
The spare tire and jack are a something like 75#, if I'm remembering right. I can do a patch kit and mini 12V compressor in the glovebox for less than 2#.
Russian roulette, but my spare and jack live in the garage, not on the truck.
Back seats, too - surprised how much they weighed.
I have 2 propane tanks, could leave one behind for short trips.
I have an access port in my water tank so I can add water anywhere from an aqua-tote. That allows me to travel with tanks low and fill up almost anywhere when I'm close to camp without having to worry about hose-access.
I'd be freaked out at traveling without jacks, but I level/ stabilize often when camping.
If I were going to be hardcore about weight, I'd take EVERYTHING out of the camper and go to the scales. I mean curtains, toilet paper... EVERYTHING. Then weigh everything that goes back in and decide if it's worth the weight item by item. As said: think like a backpacker.