It depends on how much interior you want ..... there are some on here with rear facing sink units behind the front seats ... many/most of us prefer a front to back walk-through stylee though and so most twin slider vans have the offside slider locked and the outer handle removed .
The Hulley's Bus 1989 2.1DJ Trampspotter LPG courtesy of Steve @ Gasure
we have a twin slider and absolutley love it. we used to have the units behind the front seats, and no walk through option, but we later opted to remove the bulkhead and have a walkthrough. There are some pics on my website (see signature). The timbertechs did it for us just how we wanted it. It is possible to remove the kitchen unit from behind the drivers seat to create even more space if required, and we have done this a few times whilst on longer stays. It is easy to put in the awning instead, thus allowing you to cook in a cooler environment. The thing i love about the twinslider is the fact that we can have our awning pitched on one side of the van and the wind out awning on the other side, thus giving a rather large area. Tis also a great way of cooling the van down quickly, by opening both doors at once. oh another benefit is that is doesn't matter which way you park in a camping pitch as you can use either door.
We have a twin slider and I agree with Kathy, it's great in this weather to have both doors open and keep the van cool. The biggest advantage for me, being a bit on the large side is the full width bed. We have the hob/grill/fridge behind the drivers seat and the sink/water container/gas bottle behind the passenger seat. this arrangement leaves a enough room for a narrow walk through. The down side is not much living room in the day.