That all depends upon what you think that you must have with you. The vast majority of new fulltimers carry far more "things" with them than they actually need or use. You will hear many versions of what each person needs, ranging as high as 2000# per person. I really doubt that many fulltimers would need much more than 1000# per person if they kept it to only the things actually used. We began with about 1200# each which was pushing our GVWR limits. Today, after nearly eight years we have dropped the total from the combined 2400# to slightly less than 1000# and we still have Pam's sewing machine, surger, carft stuff as well as my power tools, scroll saw and a bunch of other hobby stuff. The main thing that has lowered our total weight is that we remove anything that has been on board for 1 year and not used.
What we did was to use the bathroom scale and weigh things as we sorted as to what to carry. You need some ideas of what things will weigh before you choose how important they may be. We got cheap plastic containers that we used for storage in the larger spaces and we would load into one of them . If you have a container that is about the size of the space you are considering you can easily then know what you can put into it, fairly closely. I also suggest that you weigh the RV and get weights for each side as well as each axle, if not for each wheel. The reason is that you want to load the RV to as nearly as possible, balance it. For example, our motorhome is about 600# heavier on the right side than the left, when empty. for that reason most of my power tools are located to the left side of the storage bays. When we finished loading we again weighed the RV and the two sides were less than 150# different. That is probably as close as one is likely to get and even a person inside moving could cause it to vary that much.