Do a total clean out of your RV. Put things in piles that are similar - especially for the basement items. Then you can judge what size containers you need to purchase. Get rid of anything you haven't used the past year or two. I bet you'll find a lot of duplicates, too. When you can't find something in a jumble mess you tend to go out and buy it again.
In the basement, put like items in tubs and label them. Get tubs that you can somewhat see through which helps.
For upstairs cabinets you won't find a mess if you fill the cabinets. If you don't have enough belongings than put in rolls of paper towels or toilet paper - especially helpful for the dish cabinets. Linens also make a good packing item as will a package of napkins or paper plates. It's best to fill one cabinet completely instead of a little bit in all the cabinets. (Full-timers never have this problem) For small items, use plastic containers - a shoebox size works well for many things. Take a trip to WalMart or Target for containers of all sizes. It's best to stick with the same brand so they will stack better, if necessary.