Van exhaust?

I like the dynomax hemi super turbo. Dynomax makes a round case "rv" turbo muffler that may fit under your van. Make sure to run a full tail pipe over the axle and turned out the side. 2" is fine for the tail pipe. This will be much quieter inside (and safer from an exhaust gas entry into cabin standpoint) than a turn down or side exit exhaust.

Any "turbo" style muffler will work but the Dynomax is the best flowing. Generally any muffler with a larger case will be quieter than the same style muffler with a smaller case. Also offset inlets and outlets are quieter than centered.