we have some stuff (kitchen utensils, food) in plastic boxes (with lids) and other stuff (linen, some clothes) in the storage areas (under seat). One of our under-seat areas has a drop down access door and I've made a set of shelves to fit in there which will hold a couple of days worth of socks, jocks, shorts and t-shirts. Finding socks, etc in a duffel bag is usually a pain and you end up roughing up everything else in the bag to get at them. All our cooking stuff (pot's & pans, plates) is stored in the cupboards under the sink/bench.
For another storage area I'm going to partion so that half is used for things like our heater & iron (her idea!) and the other half will be a shoe repositry. As there's not really a huge amount of space you really need to utilise it efficiently. We're taking a porti-potti and thats taking up a lot of room, but apparently it is required!
If you get a wind-up camper, there's no room to store bags on the beds when it's folded, they'd have to go on seats or the floor. Once set-up you can put them there until bedtime, then you'll have to move them again. Not something I'd entertain. Of the trips we've done, moving stuff to get at other stuuf is a real pain. Best thing is to take less stuff so it's all got a home!